Fact-checked by Grok 2 weeks ago

Magnetic declination

Magnetic declination, also known as magnetic variation, is the angle between magnetic north—the direction indicated by a needle—and , which is the geographic direction toward the along lines of . This angle is measured in degrees and can be positive (east declination) if magnetic north lies east of , or negative (west declination) if it lies to the west. It arises from the fact that Earth's is generated by action in the molten outer core and is not aligned perfectly with the planet's rotational axis, resulting in a tilted and offset magnetic axis relative to the geographic poles. The value of magnetic declination varies significantly by geographic location, forming patterns of isogonic lines (lines of equal declination) that can be visualized on global maps, with values ranging from near zero along the agonic line (where magnetic and coincide, as of passing through the and into the ) to as much as 20–30 degrees in other regions, such as parts of the or high latitudes. Additionally, declination is not static; it changes over time due to secular variation in , with rates of change typically around 0.1–0.2 degrees per year in many areas, though faster shifts occur near the magnetic poles. These temporal changes necessitate periodic updates to navigational charts and models, as uncorrected use of a can lead to errors of several kilometers over long distances. Historically, awareness of magnetic declination emerged in Europe during the early 15th century, with initial scattered observations noted in navigational texts, though systematic recognition and measurement began in the 16th century as mariners encountered inconsistencies between compass bearings and celestial observations. Key milestones include Portuguese navigator João de Lisboa’s 1517 descriptions of variation during voyages, and the first magnetic chart, covering the Atlantic Ocean, produced by Edmond Halley in 1701, based on shipboard measurements that revealed patterns in declination across the Atlantic. By the 19th century, expeditions like Sir James Clark Ross's 1831 discovery of the North Magnetic Pole highlighted the field's dynamic nature, prompting international efforts to map and model it. In modern practice, magnetic declination is determined using a combination of ground-based observatories, satellite measurements (such as from the Swarm mission), and mathematical models like the International Geomagnetic Reference Field (IGRF) or the (WMM), which predict values to within about 1 degree of accuracy for specific dates and locations. Tools such as NOAA's online declination calculator allow users to compute it for any point on by inputting , , and date, supporting applications in , navigation, , and even smartphone compass apps. Understanding and accounting for declination remains essential for accurate orientation, particularly in regions with high variation, and ongoing monitoring helps track broader geomagnetic phenomena, including potential field reversals evidenced in paleomagnetic records spanning millions of years.

Fundamentals

Definition

Magnetic declination, often denoted as δ, is the angle at a specific location on Earth's surface between true north—the direction toward the geographic North Pole along a meridian of longitude—and magnetic north, the direction in which the north-seeking pole of a magnetic compass points. This angle arises because the Earth's magnetic field is not aligned perfectly with its rotational axis. By convention, declination is positive (east declination) when magnetic north lies to the east of true north and negative (west declination) when it lies to the west. Visually, magnetic declination represents the orientation of the horizontal component of the relative to the local meridian. If one imagines a with along the vertical axis and the horizontal magnetic field vector projected onto the horizontal plane, δ is the angle between this vector and the direction, measured clockwise from . This configuration illustrates how a needle aligns with the field's horizontal projection rather than geographic north. The declination δ is mathematically defined using the horizontal components of the magnetic field: the northward component B_x (positive toward ) and the eastward component B_y (positive toward east). It is calculated as \delta = \atan2(B_y, B_x) where is the two-argument arctangent function, yielding the angle in radians; to obtain degrees, multiply by $180/\pi. This formula ensures the correct is determined based on the signs of B_y and B_x, with δ ranging from -180° to +180°. The derivation follows from the geometry of the horizontal vector \mathbf{B}_h = (B_x, B_y), where δ is the argument of this vector in the local north-east . In practical terms, magnetic declination affects -based navigation, as an uncorrected indicates magnetic north instead of , leading to directional errors that can accumulate over distance—for example, a 10° west declination would require adding 10° to the compass bearing to obtain the true bearing. Correcting for local declination is essential for accurate orientation in activities like , , and .

Related magnetic elements

In addition to magnetic declination, which specifies the horizontal orientation of the geomagnetic field relative to true north, several other elements characterize the local magnetic field vector at any point on Earth's surface. These include the inclination (also known as the dip angle), the horizontal intensity, the total field intensity, and the vertical component. Together, these elements fully describe both the direction and strength of the geomagnetic field, enabling precise navigation and geophysical analysis. The inclination, denoted as I, is the angle between the geomagnetic field and the plane. By convention, it is measured positive downward globally; thus, it is positive in the (where the field dips downward) and negative in the (where the field dips upward). It quantifies the "dip" of the field lines into or out of the . The cosine of the inclination relates the intensity B_h to the total field intensity B via the formula \cos I = \frac{B_h}{B}, where B represents the magnitude of the full field . This relation highlights how inclination connects the and total components, with I typically ranging from 0° at the magnetic to ±90° at the magnetic poles. The horizontal intensity B_h is the magnitude of the geomagnetic field's projection onto the horizontal plane, providing a measure of the field's strength in the north-south and east-west directions. It is calculated as B_h = \sqrt{B_x^2 + B_y^2}, where B_x is the northward component and B_y is the eastward component of the field. This component is fundamental for compass-based applications, as it directly influences the horizontal force on a magnetic needle. The total field intensity B (often denoted as F) is the overall strength of the geomagnetic vector, given by B = \frac{B_h}{\cos I} or equivalently \sqrt{B_h^2 + B_v^2}, where B_v is the vertical component; typical values of B range from about 25,000 nT near the to 60,000–70,000 nT at the poles. The vertical component B_v represents the downward (positive in the ) projection of the field, essential for understanding field-line trajectories and ionospheric interactions. It is derived as B_v = B \sin I, linking it directly to the total and inclination. In vector terms, the geomagnetic field \mathbf{B} decomposes into these orthogonal components: the horizontal \mathbf{B_h} = (B_x, B_y, 0) and the vertical scalar B_v along the local , such that \mathbf{B} = (B_x, B_y, B_v). This allows the full field direction to be specified by (azimuthal angle) and inclination (polar angle), while the intensities provide the , forming a complete spherical coordinate of the local geomagnetic .

Causes

Earth's magnetic field structure

Earth's magnetic field is often approximated by a geocentric axial model, in which the behaves like a giant bar magnet with its magnetic tilted relative to the rotational . This is currently inclined at approximately 9.21° to Earth's rotation , causing the geomagnetic poles— the points where this intersects the Earth's surface—to be offset from the geographic poles. In this model, the field originates from a virtual magnetic at the 's center, producing a dominant contribution to the observed geomagnetic field that explains much of the large-scale structure responsible for magnetic declination. The magnetic field lines in the dipole approximation form closed loops emerging from the south geomagnetic pole and entering at the north geomagnetic pole, encircling the in a manner similar to a bar magnet. At any location on the surface, the field can be decomposed into and vertical components; the component, directed toward magnetic north, determines the orientation of a compass needle and thus defines the reference for measurements. This intensity varies with latitude, being strongest near the geomagnetic equator and weakening toward the poles, where the field becomes predominantly vertical. However, the actual geomagnetic field deviates from a pure due to non- contributions, which are modeled using higher-order derived from global observations. These terms, represented by Gauss coefficients up to degree and order 13 or higher in models like the International Geomagnetic Reference Field (IGRF), account for about 10-15% of the field's intensity and introduce spatial irregularities that cause local deviations in from the dipole prediction. Such complexities arise from asymmetric sources within , leading to a more intricate field structure that must be incorporated for accurate . The , defined as the location where the geomagnetic field is vertical (the dip pole), is currently positioned at approximately 86°N, 139°E and continues to drift northwestward toward at a rate of about 35 km per year as of 2025. In contrast, the north geomagnetic pole, based on the approximation, lies at about 81°N, 73°W. The distinction between these poles is crucial for understanding : the geomagnetic poles provide the baseline axis for the field, while the magnetic poles mark points of extreme inclination, with the offset and non- effects between them contributing to the angular difference observed as worldwide.

Sources of variation

Magnetic declination varies from the ideal dipolar pattern primarily due to dynamic processes within and external to Earth's . The geodynamo, driven by convective motions in the liquid outer , generates the main magnetic field through the interaction of electrically conducting fluid flows with the existing field lines, a process powered by thermal and compositional from inner core solidification and core-mantle boundary . These convective currents, influenced by via the , produce complex, time-evolving field structures that lead to secular variation in declination, with changes occurring over decades to centuries as fluid parcels advect across the core. For instance, westward drift of magnetic features at rates of about 0.2 degrees per year at the core-mantle boundary contributes to gradual shifts in declination observed globally. Crustal anomalies introduce localized perturbations to declination on scales of kilometers to hundreds of kilometers, arising from variations in the concentration and orientation of magnetic minerals, such as , within igneous, metamorphic, and rocks. These minerals, remnant of past volcanic activity or processes, create short-wavelength magnetic signatures that distort the ambient field, causing declination deviations of up to several degrees in regions like the in or the Appalachian magnetic province in . Unlike the smoother core-generated field, these anomalies are static over human timescales but must be accounted for in precise to avoid errors in readings. External influences, particularly from the and associated ionospheric currents, induce short-term variations in superimposed on the main field. The compresses Earth's and drives dynamo currents in the , producing the solar quiet () daily variation, which typically causes fluctuations of 0.1 to 0.5 degrees over a 24-hour cycle due to enhanced conductivity from solar EUV radiation. During geomagnetic storms, intensified by coronal mass ejections, ring current enhancements and auroral electrojets can amplify these effects, leading to changes of up to 1-2 degrees or more in mid-latitudes, as observed in historical events like the 1989 storm. These perturbations, lasting hours to days, arise from induced fields that temporarily alter the horizontal component of the geomagnetic field. Paleomagnetic records preserved in volcanic rocks, sediments, and ocean floor basalts reveal how past geomagnetic reversals and excursions have profoundly affected long-term patterns. During full reversals, such as the Brunhes-Matuyama event approximately 780,000 years ago, the dipolar field weakens by up to 90%, transitioning to multipolar configurations where virtual geomagnetic poles wander erratically, causing declination to swing by 180 degrees over millennia as recorded in lava flows. Shorter excursions, like the around 41,000 years ago, produce temporary declination anomalies of tens to hundreds of degrees in paleosecular variation curves derived from lake sediments, reflecting brief instabilities in core convection without full polarity flips. These records, spanning millions of years, demonstrate that declination has undergone repeated large-scale reorganizations tied to geodynamo instabilities. As of 2025, observations indicate accelerated dynamics influencing drift rates, with non-linear secular variation pulses linked to rapid fluid flow changes in the outer , including six such events detected since 2000 (in 2006, 2009, 2012, 2016, 2018, and 2021), each lasting 2-3 years and strongest at low latitudes. The 2025, incorporating satellite and ground data up to October 2024, forecasts continued elevated secular variation, with global root-mean-square errors projected at 0.41 degrees by 2030, reflecting these dynamic processes amid ongoing weakening. This acceleration contributes to faster poleward drift of the magnetic at approximately 35 km per year, indirectly amplifying regional changes.

Variation Patterns

Spatial distribution

Magnetic declination varies significantly across Earth's surface, as depicted by isogonic lines on global maps, which connect points of equal and illustrate the angular difference between magnetic north and . These lines form irregular contours influenced by the geomagnetic field's structure, with intervals typically spaced at 2 degrees for visualization. The agonic line, where is zero, serves as a reference where magnetic and align, and isogonic lines converge toward it from both sides. According to the 2025 (WMM2025), the agonic line currently extends from southward through the central United States—passing near the and into the —before curving toward in the . Global patterns of declination reveal distinct regional characteristics based on the WMM2025. In , values range from near zero along the agonic line to positive (east) declinations of up to 15° in the , such as approximately +15° near , while eastern areas like exhibit slight negative (west) values around -3°. In Asia, declination is predominantly negative, reaching about -9° in , . Europe shows small negative to positive values, typically 0° to +2° in the . These patterns reflect the offset between the geomagnetic and geographic poles, with the magnetic north pole's position contributing to broader east declinations in the and west declinations in . In polar regions, the spatial distribution of declination becomes highly anomalous due to the near-vertical of the near the dip poles. Here, the horizontal field intensity drops below 6000 in caution zones and under 2000 in blackout zones, rendering declination practically irrelevant for as the needle may not align horizontally. The WMM2025 identifies such zones around the and , where rapid spatial gradients complicate patterns. Hemispheric differences are pronounced, with declination generally exhibiting opposite signs north and south of the owing to the geomagnetic dipole's 11° tilt relative to Earth's rotational ; for instance, positive values dominate the northern hemisphere's western sectors, while negative values prevail in the southern hemisphere's eastern sectors. Crustal anomalies can locally perturb these patterns, though their effects are minor compared to core-generated fields.

Temporal changes

Magnetic declination exhibits temporal changes across various timescales, driven primarily by the dynamics of Earth's and external influences from solar activity. On long timescales, secular variation represents the primary mode of change, characterized by a gradual drift in the direction of the . This drift typically occurs at rates of 0.1° to 0.5° per year, varying by location due to the westward propagation of non-dipolar field components. For instance, at , historical records indicate a declination of approximately 11° east in , which shifted to near zero by 2020, reflecting a net westerly progression over four centuries influenced by core fluid motions. Short-term fluctuations in declination occur on diurnal and storm timescales, superimposed on the secular trend. Diurnal variations, induced by ionospheric currents driven by solar heating and activity, can reach amplitudes of up to 1° at mid-latitudes, with the compass needle oscillating around its mean position throughout the day. During geomagnetic storms—intense disturbances triggered by solar coronal mass ejections—these variations intensify, causing temporary deflections observable with a sensitive , often exceeding 0.5° and lasting hours to days as interacts with the . Over intermediate timescales, declination is modulated by periodic cycles and abrupt events. The 11-year solar cycle influences geomagnetic variations through enhanced solar wind and interplanetary magnetic field fluctuations, subtly affecting declination ranges by up to 10-20% in amplitude at certain observatories. Longer-term irregularities include geomagnetic jerks, sudden accelerations or decelerations in the secular variation occurring every 3-12 years, originating from impulsive changes in core flows that alter the field's evolution rate by factors of 2-3 in affected regions. Current predictive models, such as the International Geomagnetic Reference Field (IGRF-13) and , forecast an average global drift of about 0.2° per year through 2030, with accelerations in high-latitude areas linked to the ongoing northward drift of the magnetic toward at reduced speeds of 20-30 km/year post-2020. These forecasts incorporate post-2020 satellite data from missions like , highlighting increased uncertainty in polar regions due to core-mantle boundary dynamics.

Determination Methods

Field measurements

Field measurements of magnetic declination involve direct on-site determination of the angle between magnetic north and true north using specialized instruments to capture the horizontal components of the Earth's magnetic field, denoted as B_x (northward) and B_y (eastward), where declination D = \tan^{-1}(B_y / B_x). In the 19th century, early field measurements relied on instruments like the dip circle and deflection magnetometer. The dip circle, consisting of a magnetic needle pivoted at its center within a vertical graduated circle, primarily measured inclination but included an auxiliary pivoted needle for determining declination by aligning it with the magnetic meridian relative to true north. The deflection magnetometer, developed by Carl Friedrich Gauss around 1832, used a small test magnet to measure the horizontal field intensity through deflection angles, aiding declination determination by establishing the magnetic meridian through successive alignments. These methods required manual observation and were limited to accuracies of several degrees due to instrumental and observational constraints. Modern field measurements predominantly employ vector magnetometers, such as fluxgate types, to precisely measure the B_x and B_y components. Fluxgate magnetometers, like the Bartington Mag-01H system, integrate a three-axis fluxgate with a non-magnetic to detect field directions with resolutions better than 0.1°. Proton magnetometers, while scalar instruments measuring total field intensity, are sometimes used in tandem with fluxgate sensors for comprehensive vector profiling in field surveys. The standard procedure begins with establishing through astronomical observations, such as sighting the sun at local noon or polar stars like at night, using a or transit for precise alignment. The magnetometer sensor is then mounted on the theodolite and rotated to align with the , where the field components are recorded; is computed from the angular offset between this alignment and the true north reference. This DI-fluxgate method, refined since the mid-20th century, achieves absolute accuracies of 0.05° to 0.1° under ideal conditions. Portable modern devices, including apps leveraging built-in magnetometers, enable approximate measurements with typical directional accuracies of 1° after . These apps compute declination by processing triaxial sensor data against known models but require manual verification against for reliability. Key error sources in measurements include local magnetic from objects, vehicles, or power lines, which distort the ambient and can introduce deviations up to several degrees. involves selecting non-magnetic sites, such as open distant from structures (at least 100 m from metal sources), and conducting pre-measurement surveys to levels.

Maps and charts

Magnetic declination is commonly accessed through published geomagnetic charts known as isogonic maps, which depict lines connecting points of equal declination across geographic regions. These maps enable navigators, surveyors, and researchers to determine the local angle between magnetic and true north without direct measurement. The earliest notable example is Edmond Halley's 1701 chart of the Atlantic Ocean, the first to illustrate isogonic lines based on systematic observations during his voyages from 1698 to 1700, marking a pioneering effort to visualize global magnetic variation patterns. Contemporary world declination charts are generated by the National Centers for Environmental Information (NCEI) using the (WMM), a collaborative effort between NOAA and the . The WMM produces isogonic maps updated every five years to reflect secular changes in , with the WMM2025 version released on December 17, 2024, valid from 2025 to 2030. These charts show declination contours at intervals such as 2 degrees, often in projections like the Miller cylindrical, allowing global assessment of values ranging from over 30° east in parts of to more than 60° west near the magnetic poles. Regional charts provide finer detail for specific areas, such as the , where exhibits notable spatial gradients. For instance, under the WMM2025, values in 2025 approximate 14° west in northern and 13° west in , illustrating the westward bias across much of the continental U.S. while highlighting subtle variations due to local field anomalies. Interpreting these charts involves locating the position on the and estimating the by or between adjacent isogonic lines, a method that yields accuracy typically within 1° for most applications. For positions near the zero agonic line—where magnetic and align—charts emphasize this boundary to aid precise . Digital tools enhance accessibility to these charts and computations, with NOAA's online Magnetic Declination Calculator allowing users to input , , and date for instantaneous values derived from the WMM or International Geomagnetic Reference Field (IGRF) models. This resource supports both historical queries from 1900 onward and projections up to 2030, complementing static maps for real-time or location-specific needs.

Mathematical models and software

The International Geomagnetic Reference Field (IGRF) is a standard representing the Earth's main and its secular variation, derived from global observations including satellite, , and survey data. It employs a spherical expansion of the geomagnetic up to and 13 (since 1995), allowing computation of field components at any point on or above the Earth's surface. The potential V(r, \theta, \phi, t) is given by V(r, \theta, \phi, t) = a \sum_{n=1}^{13} \sum_{m=0}^{n} \left( \frac{a}{r} \right)^{n+1} \left[ g_n^m(t) \cos(m\phi) + h_n^m(t) \sin(m\phi) \right] P_n^m(\cos\theta), where a is the Earth's reference radius (typically 6371.2 km), r is the radial distance, \theta is the colatitude, \phi is the longitude, t is time, g_n^m(t) and h_n^m(t) are the Gauss coefficients (updated every five years), and P_n^m are the associated Legendre functions. The magnetic field components in spherical coordinates are then B_r = -\partial V / \partial r, B_\theta = -(1/r) \partial V / \partial \theta, and B_\phi = -(1/(r \sin\theta)) \partial V / \partial \phi. Magnetic declination D is calculated from the horizontal components as D = \atantwo(B_y, B_x), where B_x and B_y are the north and east components in a local Cartesian frame derived from B_\theta and B_\phi. The World Magnetic Model (WMM), developed jointly by the US National Geospatial-Intelligence Agency (NGA) and the UK Defence Geographic Centre (DGC) in collaboration with NOAA, serves as the practical implementation of the IGRF specifically tailored for navigation applications. It uses the same spherical harmonic framework up to degree 12 for the main field and degree 8 for secular variation, with coefficients aligned to IGRF epochs but optimized for operational use in systems like compasses and GPS devices. The WMM2025 edition, released in December 2024, is valid from 2025 to 2030 and incorporates updated coefficients to account for recent field changes, ensuring compatibility with military, aviation, and maritime standards. A high-resolution variant, WMMHR2025, was introduced in 2025 for enhanced detail in regional applications. Software tools for computing magnetic declination from these models typically require inputs of geographic , , altitude, and date, outputting along with other field elements. NOAA's National Centers for Environmental Information (NCEI) provides an online geomagnetic based on both IGRF and WMM, supporting access for programmatic use and delivering results in various formats. Open-source alternatives include PyGeomag, a library implementing the WMM algorithm for efficient field synthesis, suitable for integration into scientific workflows or custom applications. Recent iterations of the IGRF, such as the 14th generation (valid through 2030.0), incorporate data from the European Space Agency's , enhancing model fidelity at high latitudes where external field influences are pronounced. These models achieve typical accuracies of about 0.5° (30 arcminutes) for declination predictions over five-year epochs, though local crustal anomalies or rapid secular changes may require empirical corrections for higher precision.

Compass Adjustments

Rotating dial compasses

Rotating dial compasses employ a rotatable or capsule mechanism that permits users to mechanically compensate for magnetic by offsetting the dial relative to the magnetic needle. This allows the instrument to display bearings directly when the needle aligns with magnetic north. The adjustment process begins with determining the local magnetic value. Users then rotate the dial—typically via a small on the base or side—to shift the orienting arrow or north index by the declination angle; for example, with a 10° east declination, the dial is turned clockwise by 10° to add the offset, ensuring magnetic readings convert automatically to true bearings. Such compasses are prevalent in and applications, including Suunto models like the MC-2 series, which use a bottom adjustment screw to align the north arrow, and Brunton models like the TruArc, featuring tool-less rotation of the capsule. This design offers simplicity for field users, enabling straightforward navigation without repeated mental arithmetic once set for a . However, it requires manual readjustment upon moving to areas with different declination values, as the angle varies spatially. Historically, the rotating dial adjustment for declination originated in 19th-century survey instruments, exemplified by the Brunton pocket transit patented in 1894 by geologist David W. Brunton to facilitate precise mining surveys.

Card and liquid compasses

Card and liquid compasses feature a magnetic card, typically a lightweight disk or dome inscribed with degree markings, suspended on a central pivot within a sealed bowl filled with damping fluid such as alcohol-water mixtures or kerosene derivatives. This design allows the card to rotate freely in response to the Earth's magnetic field while the fluid minimizes oscillations and friction, providing smoother readings compared to dry pivot systems. The pivot, often a hardened steel point with a jewel bearing, supports the card's weight, and a gimbal mounting in marine and aviation models permits limited tilt—up to 18 degrees in aircraft—to maintain horizontal orientation during motion. These compasses are prevalent in marine navigation for their reliability on vessels and in aviation for required VFR/IFR operations, with variants incorporating gyro-stabilization to enhance heading stability by slaving the magnetic sensing to a gyroscopic reference. Adjustments for magnetic declination in these primarily involve index correction to align the lubber's line—the fixed reference mark on the —with the vehicle's fore-and-aft , eliminating inherent errors. itself is accounted for via external charts or by adding/subtracting the value from magnetic readings during calculations, rather than internal mechanical adjustment, as the inherently points to magnetic north. Compensation for deviation (separate from ) uses built-in magnets or spheres. In some integrated systems, electronic offsets can be applied for correction. For example, nautical like the Weems-Plath models or Ritchie Voyager series incorporate these features for direct marine use, with diaphragms to handle fluid expansion. The calibration procedure begins with establishing a known true bearing, such as from a , sun , or GPS-derived heading, then comparing it to the magnetic reading to compute as δ = true bearing minus . This value is then used in by adjusting magnetic headings accordingly; for instance, in marine settings, observations from the provide the true reference, with local variation applied from charts like Pub. No. 229. These compasses offer advantages in dynamic environments, where the liquid damping—enhanced by baffles or filaments attached to the card—provides rapid settling and stability during pitching, rolling, or acceleration, outperforming undamped designs in and applications. Systems like Ritchie's PowerDamp® further reduce in high-speed or rough conditions, maintaining without power dependency. Limitations include sensitivity to temperature variations, which can cause fluid expansion or contraction, potentially forming bubbles that impair card movement if not mitigated by expansion diaphragms; extreme temperatures may also alter magnetic properties slightly. Additionally, while gimbals aid stability, excessive tilt beyond design limits—such as over 18 degrees in —can introduce errors, and the sealed design requires periodic professional servicing to prevent leaks.

Navigation Applications

Deviation correction

Compass deviation refers to the error in a magnetic compass reading caused by local magnetic influences from onboard ferrous materials, electrical currents, or equipment in vehicles such as ships or , which deflects the compass needle from the magnetic and varies depending on the vehicle's heading. For example, deviation might amount to +5° when heading east but -3° when heading north, distinguishing it from the geographically fixed magnetic declination. The primary causes of deviation are hard iron effects, arising from permanent in magnetized components like tools or engine parts, which produce semicircular deviations, and soft iron effects, from induced in structures that generate quadrantal deviations varying with the . To correct for deviation, a process known as swinging the vessel or is performed by aligning the vehicle on multiple headings—typically (0°, 90°, 180°, 270°) and intercardinal (45°, 135°, 225°, 315°)—and comparing the reading to a known true heading derived from observations, GPS, or visual references, allowing technicians to adjust compensators such as magnets or soft iron spheres to minimize errors. The relationship, using signed values (positive for easterly errors, negative for westerly), is given by the equation: \text{True bearing} = \text{Observed compass bearing} + \text{Deviation} + \text{Declination} from which deviation is isolated as \text{Deviation} = \text{True bearing} - \text{Observed compass bearing} - \text{Declination}. This follows the convention where easterly declination and deviation are added to the compass bearing to obtain true bearing, and westerly values are subtracted (mnemonic: "True = Variation + Magnetic"; "Magnetic = Deviation + Compass"). Residual deviations after adjustment are recorded in a deviation correction table or card, listing errors for key headings (often in 30° increments for ), which navigators use to apply manual corrections during operation. Standard practice requires recalibration annually for vessels, or more frequently after structural alterations, major equipment installations, or significant changes in magnetic latitude, to ensure navigational accuracy.

Marine navigation

In marine navigation, Admiralty charts produced by the Hydrographic Office (UKHO) incorporate magnetic declination information through compass roses that display the current variation value and its rate of change, enabling mariners to plot accurate courses by adjusting magnetic bearings to over time. These roses typically feature an inner magnetic rose aligned to magnetic north and an outer true rose aligned to geographic north, with the angular difference marked as the declination, often printed in for visibility; the change, usually expressed in minutes per year (e.g., increasing or decreasing), allows for future years using the : updated variation = base variation + ( change × years elapsed). This integration ensures that navigators can apply corrections directly during voyage planning and execution on paper or raster charts. Modern vessels primarily rely on gyrocompasses, which maintain alignment with via the and do not require corrections, providing a stable primary heading reference for steering and automated systems like autopilots. However, the magnetic compass serves as a critical backup in case of gyrocompass failure, such as power loss or mechanical issues, and its readings must be corrected for (δ) to convert magnetic headings to true headings using the mnemonic "true virgins make dull company" (True = Variation + Magnetic, where variation is , added if east and subtracted if ). This correction is essential during voyages where failures could occur, ensuring in heading determination. Under the International Convention for the Safety of Life at Sea (SOLAS) Chapter V, Regulation 19, all ships irrespective of size must carry a properly adjusted standard , and for ships of 150 gross tons and upwards, a deviation card detailing residual errors after adjustment must be prominently displayed on the bridge and updated annually or after significant structural changes. This requirement, outlined in Resolution A.382(X), mandates that the deviation table include headings at intervals of no more than 15 degrees, with verification by a certified adjuster to comply with performance standards. Historical incidents in the underscore the dangers of unadjusted deviation in iron ships; for instance, the 1854 wreck of the iron Tayleur off the coast of , which resulted in over 200 fatalities, was partly attributed to compass deviation from the iron and . Similarly, the 1859 sinking of the Royal Charter near , claiming 459 lives, occurred during a severe but highlighted ongoing issues with compass deviation in iron vessels, leading to mid-19th-century reforms in compass regulation and adjustment practices. These cases emphasized the need for proper deviation corrections in varying conditions. As of 2025, the (IMO) guidelines for Electronic Chart Display and Information Systems (ECDIS) under SOLAS V/19.2.10 require incorporation of the updated World Magnetic Model (WMM2025), released in December 2024 by the National Geospatial-Intelligence Agency (NGA), National Centers for Environmental Information (NCEI), and (BGS), to provide accurate real-time declination data for automatic correction in digital . The release also included the first World Magnetic Model High Resolution (WMMHR2025), offering enhanced spatial resolution (300 km vs. 3300 km) for improved local predictions in systems. This model, valid until 2030, enhances precision in electronic charts by modeling secular variation with coefficients up to and order 12 for the core field, ensuring that ECDIS software applies location-specific δ values during route planning and collision avoidance, with mandatory updates to avoid discrepancies in high-latitude or polar regions where declination can exceed 60 s. Mariners must verify WMM integration during system commissioning and annual performance tests to meet IMO MSC.1/Circ.1509 standards for navigational accuracy.

Aviation navigation

In aviation navigation, magnetic declination plays a critical role in aligning headings with ground-based aids like (VOR) and (ILS) stations, which transmit signals referenced to magnetic north. Pilots must adjust these magnetic bearings to true headings by applying the local declination value during and execution, ensuring accurate course tracking and approach alignment. For instance, when intercepting a VOR radial or following an ILS localizer, the displayed magnetic course requires conversion to for integration with GPS or inertial systems that operate on true references. The (FAA) incorporates data into sectional aeronautical charts through isogonic lines, which delineate areas of equal magnetic variation and provide specific values for . These lines, updated based on the World Magnetic Model's five-year epoch, enable pilots to determine the necessary adjustments for routes; for example, in 2025, much of the experiences an average variation of about 3–5° west. This visual aid is essential for VFR and IFR , where pilots subtract easterly (or add westerly) to convert true headings to magnetic for or VOR use. Electronic fluxgate compasses, common in modern heading reference systems, detect the to provide magnetic heading data, which avionics suites automatically correct for declination using position-derived values from navigation databases. These systems adhere to standards, such as for data transmission, ensuring seamless integration with flight management systems (FMS) that compute true headings by adding the local variation—typically sourced from models like WMM2025—to mitigate errors in high-speed operations. Fluxgate sensors thus support slaved gyroscopic instruments, reducing pilot workload while maintaining accuracy within tolerances like the FAA's ±5° for VOR variation. On polar routes, where the magnetic north pole's proximity causes rapid declination changes—up to 180° over short distances—traditional magnetic becomes unreliable, often exceeding ° variation and rendering compasses erratic. Pilots rely on GPS overrides and grid navigation, which uses a fixed reference grid aligned to , to maintain safe headings; this shift is particularly vital for transpolar flights between and , where inertial navigation systems () supplement GNSS to avoid deviation errors. In response to these challenges and the increasing reliability of Global Navigation Satellite Systems (GNSS), the (ICAO) has advanced updates in 2025 through its True North Advisory Group (TRUE-AG), promoting a phased transition from magnetic to references in global navigation specifications. This initiative, outlined in ICAO Assembly discussions, aims to phase out reliance on magnetic declination by standardizing true headings in procedures and databases, favoring GNSS for precision and reducing update burdens from secular variation—expected to culminate in revised Annex 11 standards by the late 2020s.

References

  1. [1]
    Magnetic Declination - National Centers for Environmental Information
    Magnetic declination (sometimes called magnetic variation) is the angle between magnetic north and true north. Declination is positive when this angle is east ...
  2. [2]
    What is declination? | U.S. Geological Survey - USGS.gov
    The deviation of the compass from true north is an angle called "declination" (or "magnetic declination"). It is a quantity that has been a nuisance to ...
  3. [3]
    Geomagnetism Frequently Asked Questions
    25 - .65 gauss). Magnetic declination is the angle between magnetic north and true north. D is considered positive when the angle measured is east of true north ...
  4. [4]
    Earth's Magnetic Declination - Science On a Sphere - NOAA
    Jan 1, 2010 · This dataset shows lines of equal magnetic declination (isogonic lines) measured in degrees east (positive) or west (negative) of True North.
  5. [5]
    Tracking Changes in Earth's Magnetic Poles | News
    Mar 28, 2016 · Our Historical Magnetic Declination Map Viewer shows changes in Earth's magnetic field and geomagnetic poles from 1590 to 2020.
  6. [6]
    [PDF] Four centuries of geomagnetic secular variation from historical records
    Awareness of magnetic declination dates back to the first half of the 15th cen- tury, at least in Europe. These fi rst measurements take the form of scattered ...
  7. [7]
    Help: Magnetic Declination Calculator | NCEI - NOAA
    Declination: The angle of difference between true North and magnetic North. For instance, if the declination at a certain point were 10° W, then a compass at ...
  8. [8]
    More Information About Geomagnetic Fields | NCEI - NOAA
    By convention, declination is considered positive when measured east of north, inclination and vertical intensity positive down, X positive north, and Y ...Missing: atan2 | Show results with:atan2
  9. [9]
    igrf12.f
    ... declination (+ve east)'/ 1 ' I is inclination (+ve down)'/ 2 ' H is ... ATAN2(Y,X) H = SQRT(X*X + Y*Y) S = FACT*ATAN2(Z,H) CALL DDECDM (D,IDEC,IDECM) ...
  10. [10]
    Magnetic components
    Magnetic components ; X · the north component of the magnetic field; X is positive northward ; Y · the east component of the magnetic field; Y is positive eastward.Missing: atan2 | Show results with:atan2
  11. [11]
    What are the geomagnetic components ? - Intermagnet
    Magnetic components​​ the magnetic declination, defined as the angle between true north (geographic north) and the magnetic north (the horizontal component of ...Missing: atan2 | Show results with:atan2
  12. [12]
    An Overview of the Earth's Magnetic Field - BGS Geomagnetism
    The Earth's magnetic field has components X, Y, and Z, and is described by total intensity F, horizontal intensity H, inclination I, and declination D. The  ...
  13. [13]
    Wandering of the Geomagnetic Poles
    Magnetic poles are commonly understood as positions on Earth's surface where the geomagnetic field is vertical (i.e., perpendicular) to the ellipsoid.Historical Magnetic Declination · North Dip Poles · South Dip Poles
  14. [14]
    World Magnetic Model (WMM)
    The seven magnetic components computed are: F: Total Intensity of the geomagnetic field; H: Horizontal Intensity of the geomagnetic field; X: North Component of ...Magnetic Model Survey · WMMHR Home Page · Wandering Geomagnetic Poles<|control11|><|separator|>
  15. [15]
    A Spherical Harmonic Model of Earth's Lithospheric Magnetic Field ...
    Oct 21, 2021 · A global model that represents the magnetic field generated within the Earth's crust with a global 40 km horizontal spatial resolution.
  16. [16]
    International Geomagnetic Reference Field (IGRF)
    The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the Earth's main magnetic field.Missing: drift | Show results with:drift
  17. [17]
    Geomagnetic secular variation forecast using the NASA GEMS ...
    Feb 11, 2021 · This change, called the secular variation (SV), originates dominantly from the Earth's iron-rich fluid outer core that is vigorously convecting, ...Missing: liquid declination
  18. [18]
    [PDF] The Magnetic Field of the Earth
    The resulting buoyancy drives compositional convection in the outer core, and the combination of convection and rotation produces the complex motion needed.
  19. [19]
    Gyre-driven decay of the Earth's magnetic dipole - Nature
    Jan 27, 2016 · The Earth's magnetic field is generated by a dynamo operating within the liquid metal outer core. Here fluid motions stretch, twist, and ...Missing: declination | Show results with:declination
  20. [20]
    [PDF] Calculating depths to shallow magnetic sources using aeromagnetic ...
    Anomalies in the geomagnetic field are mainly caused by variations in the presence of a small proportion of magnetic minerals found in the underlying rocks.Missing: perturbations | Show results with:perturbations
  21. [21]
    [PDF] Aeromagnetic Surveys
    Ferrimagnetic magnetite accounts for only about 1.5 percent of crustal minerals and is by far the most important magnetic mineral in geophysical mapping (Clark.
  22. [22]
    Introduction to Geomagnetism | U.S. Geological Survey - USGS.gov
    Time-dependent magnetic-field variations sustained by currents in the ionosphere and magnetosphere induce electric currents in the crust, ocean, and mantle.
  23. [23]
    [PDF] 130617 PARC Magnetic Variation Recommendations
    Jun 17, 2013 · worst-case scenario for the magnetic declination during an extreme magnetic storm in 2015 is 3.24 degrees. Table 3 Estimated RMS ...
  24. [24]
    [PDF] Chapter 8: Earth's Geomagnetic Environment.
    This daily variation in the magnetic field is called Sq, for “solar quiet”, because it is best seen in the absence of magnetic storms and other solar ...
  25. [25]
    Is it true that Earth's magnetic field occasionally reverses its polarity?
    The deviation of the compass from true north is an angle called "declination" (or "magnetic declination"). It is a quantity that has been a nuisance to ...Missing: definition | Show results with:definition<|control11|><|separator|>
  26. [26]
    Rapid geomagnetic changes inferred from Earth observations and ...
    Jul 6, 2020 · Paleomagnetic studies have reported rapid directional changes reaching 1° yr−1, although the observations are controversial and their relation ...
  27. [27]
    Rapid geomagnetic changes inferred from Earth observations and ...
    Jul 6, 2020 · Overall, it has proved difficult to substantiate extremely rapid changes in individual paleomagnetic records either during reversals or at other ...
  28. [28]
    [PDF] The US/UK World Magnetic Model for 2025-2030
    Jan 14, 2021 · This report provides a comprehensive description of the World Magnetic Model (WMM) 2025 and its higher- resolution version, the World ...
  29. [29]
    World Magnetic Model 2025 Released | News
    Dec 17, 2024 · The World Magnetic Model 2025 (WMM2025) provides more precise navigational data for all military and civilian planes, ships, submarines, and GPS units.WMM · Tracking Changes in Earth’s... · Geomagnetism
  30. [30]
    Magnetic Declination in Beijing, China
    Answer: -9.25° (-9°15') ... Cosmos Plus! ... Magnetic declination is calculated using the World Magnetic Model WMM2025.
  31. [31]
    [PDF] US/UK World Magnetic Model - Epoch 2025.0 Main Field ...
    This is the US/UK World Magnetic Model for Epoch 2025.0, showing Main Field Declination (D), developed by NOAA/NCEI and CIRES, published December 2024.
  32. [32]
    Secular Variation - an overview | ScienceDirect Topics
    Secular variation refers to the slow changes in the Earth's magnetic field components over time, characterized by a westward drift of approximately 0.2° ...
  33. [33]
    Magnetic Variation - an overview | ScienceDirect Topics
    He noted that whereas Borough in 1580 had measured a value of 11.3°E for the declination at London, his own measurements in 1634 gave only 4.1°E. The difference ...
  34. [34]
    MAGNETIC DECLINATION - Earth Science Australia
    These magnetic storms will interfere with radio and electric services, and will produce dazzling spectacles of auroras. The varied colors are caused by oxygen ...<|separator|>
  35. [35]
    Does a geomagnetic storm visibly deflect a compass?
    Feb 25, 2020 · You can definitely see a large geomagnetic storm with a compass, if you have the timing to catch one and the patience to sit and stare for a few minutes.
  36. [36]
    The effect of solar activity on the secular variation of the ...
    The 11-year solar cycle effect in the geomagnetic components H and Z is made clear for Surlari Observatory and 19 repeat stations for the interval 1952–1974.
  37. [37]
    Swarm helps explain Earth's magnetic jerks - ESA
    May 1, 2019 · The jerks originate in rising blobs of metal that form in the planet's core 25 years before the corresponding jerk takes place. These current ...
  38. [38]
    BGS leads update to maps of the Earth's magnetic field
    Apr 4, 2024 · The geomagnetic community also makes an estimate of how the magnetic field will change between 2025 and 2030. In 2030, this process will be ...Missing: post- | Show results with:post-
  39. [39]
    Lloyd-Creak Dip Circle | National Museum of American History
    An auxiliary needle on top is used to determine magnetic declination. Ref: Carnegie Institution of Washington. Department of Terrestrial Magnetism, Land ...
  40. [40]
    The instruments of expeditionary science and the reworking of ...
    Mar 30, 2022 · First, there was magnetic variation, or 'declination', being the difference between magnetic north as shown by a compass and geographic north ...
  41. [41]
    https://royalsocietypublishing.org/doi/10.1098/rsnr.2022.0002
  42. [42]
    [PDF] Operation Manual - Geometrics
    The proton precession magnetometer is one of the principal instruments for magnetic surveys because it combines high accuracy and ease of use.
  43. [43]
    [PDF] Chapter 10 Measuring the Earth's magnetic field
    The declination and inclination of the magnetic field are measured with a DI-flux- magnetometer, which consists of a non-magnetic Zeiss-Jena theodolite (010B) ...
  44. [44]
    http://helios.fmi.fi/~juusolal/geomagnetism/Lectures/Chapter10_measurement.pdf
  45. [45]
    Mag-01H DI - Bartington Instruments
    The Mag-01H Declinometer/Inclinometer system provides rapid, reliable and accurate measurements of the declination and inclination of the geomagnetic field.
  46. [46]
    Robust Determination of Smartphone Heading by Mitigation of ...
    In experiments with very accurate ground truth, the proposed algorithm achieves a root mean square error of 17.4° for the computed heading, outperforming state- ...
  47. [47]
    Assessment of the precision of smart phones and tablets for ...
    This paper deals with this question through detailed tests of two android devices: an Honor 3C smartphone and a Lenovo B8080-F tablet.Missing: declination | Show results with:declination
  48. [48]
    World Magnetic Model Accuracy, Limitations, and Error Model
    Some local, regional, and temporal magnetic declination anomalies can exceed 10 degrees. Anomalies of this magnitude are not common but they do exist.
  49. [49]
    How to Navigate Safely Despite Magnetic Compass Disturbances
    Dec 20, 2023 · Disturbances to a magnetic compass can arise from factors like ferrous objects, electromagnetic interference, temperature variations, and external forces.
  50. [50]
    Mapping Magnetism | Worlds Revealed - Library of Congress Blogs
    May 23, 2025 · World map showing isogonic lines of magnetic declination and the location of the magnetic north pole Photo by author. A Chart of Magnetic ...
  51. [51]
    Magnetic Declination Contours (2 degrees - 1590-2030)
    Mar 13, 2025 · This layer displays isogonic lines (lines of magnetic declination) calculated for the years 1590-2030, with a 2-degree interval. Model ...
  52. [52]
    NOAA Mobile Magnetic Declination Calculator
    △ ; Longitude: W E ; Altitude: ; January; February; March; April; May; June; July; August; September; October; November; December. 01; 02; 03; 04; 05; 06; 07; 08 ...Missing: atan2 | Show results with:atan2
  53. [53]
    Magnetic Declination (Variation) | NCEI - NOAA
    Magnetic declination, sometimes called magnetic variation, is the angle between magnetic north and true north. Declination is positive east of true north ...Missing: definition | Show results with:definition
  54. [54]
    The secrets behind a compass: What are agonic and isogonic lines?
    Nov 8, 2024 · An agonic line is defined as 'an imaginary line around the earth passing through both the north pole and the north magnetic pole, at any point ...
  55. [55]
    Magnetic Declination Varies Considerably Across The United States
    Magnetic declination is the direction and amount of variation between the Magnetic Pole and True North. The amount and direction of declination depends upon how ...
  56. [56]
    International Geomagnetic Reference Field: the thirteenth generation
    Feb 11, 2021 · The main field coefficients are not yet known for T t = 2025 , and so for the final 5 years of model validity (2020 to 2025 for IGRF-13), the ...
  57. [57]
    pyGeoMag is an implementation in Python of the World ... - GitHub
    Declination is the angle that adjusts a compass reading from Magnetic North to True North. Many maps will show it in the legend, so you can adjust your compass ...
  58. [58]
    NCEI Geomagnetic Calculators
    ### Summary of Magnetic Field Calculators (https://www.ngdc.noaa.gov/geomag-web/)
  59. [59]
    Magnetic reference field models
    It is generally agreed that the IGRF achieves an overall accuracy of better than 1° in declination; the accuracy is better than this in densely surveyed areas ...
  60. [60]
    Adjustable Declination Compasses | U.S. Geological Survey
    A compass with adjustable declination allows you to rotate the orienting arrow independently of the compass dial.Missing: mechanism | Show results with:mechanism
  61. [61]
    How to Adjust Compass Declination | REI Expert Advice
    You have to understand what it means and how to set the declination on your compass properly. This article guides you through that process.<|separator|>
  62. [62]
    Map & Compass: Adjust for declination & orient the map
    Jul 16, 2016 · With an adjustable compass, the orienting arrow (“the shed”) can be rotated relative to the bezel by twisting a small screw on the back of the compass.Missing: mechanism | Show results with:mechanism
  63. [63]
    Understanding declination correction - Suunto
    Adjustable declination correction is set once when starting to navigate by turning the North arrow in the bottom of the capsule to the angle that corresponds ...
  64. [64]
    https://andrewskurka.com/map-compass-adjust-for-declination-orient-the-map/
  65. [65]
    https://www.suunto.com/Support/Compasses-feature-index/Understanding-declination-correction/
  66. [66]
    The Brunton Standard Transit Compass – 100% Made In The USA
    Apr 12, 2023 · The Brunton compass was invented in 1894 by Canadian-born geologist and mining engineer, David W. Brunton. While working in the mineral-rich ...Missing: date | Show results with:date
  67. [67]
    THE BRUNTON POCKET TRANSIT, A ONE HUNDRED YEAR OLD ...
    Aug 30, 2022 · On September 18, 1994, Brunton's Patent Pocket Mine Transit, and its descendents, completed one hundred years of distinguished geological ...
  68. [68]
    [PDF] Chapter 8 - Flight Instruments - Federal Aviation Administration
    The adjustments position the compensating magnets to minimize the difference between the compass indication and the actual aircraft magnetic heading. The AMT ...<|separator|>
  69. [69]
    [PDF] Ritchie's Complete Guide to Compass Navigation
    Enhance the steady performance of the Ritchie compass. Baffle reduces turbulence in the dampening fluid, while diaphragm allows fluid to expand or contract with ...Missing: advantages limitations
  70. [70]
    [PDF] HANDBOOK OF MAGNETIC COMPASS ADJUSTMENT
    It consists of a magnetized needle, or array of needles, pivoted so that rotation is in a horizontal plane. The superiority of the present day compass results ...
  71. [71]
    [PDF] AC 43-215 - Standardized Procedures for Performing Aircraft ...
    Aug 7, 2017 · Compass calibration typically involves two steps. First, compass compensators are adjusted to minimize the influence of aircraft-induced fields ...Missing: declination | Show results with:declination
  72. [72]
    [PDF] Chapter 16 - Navigation - Federal Aviation Administration
    To determine compass heading, a correction for deviation must be made. Because of magnetic influences within an aircraft, such as electrical circuits, radio, ...
  73. [73]
    ADMIRALTY Reference and Plotting Charts
    Magnetic Variation Charts ... Six charts which show the current magnetic variation and the annual rates of change. Whilst local information is shown on all charts ...
  74. [74]
    [PDF] Magnetic Compass in Modern Maritime Navigation - TransNav Journal
    Dec 4, 2015 · The magnetic compass is a highly reliable and cheap indicator of ship's course. It is a very good solution to the problem of gyrocompass ...
  75. [75]
    [PDF] A.382(X) adopted on 14 November 1977 MAGNETIC COMPASSES ...
    Dec 15, 1977 · The minimum distances of the standard compass from any magnetic material which is part of the ship's structure should be to the satisfaction of ...
  76. [76]
    Maintaining magnetic compasses onboard: All you need to know
    Nov 20, 2023 · According to SOLAS amendments, the use of a magnetic compass is mandatory. The magnetic compass must adhere to the standards set forth by ...Missing: length | Show results with:length
  77. [77]
    Mrs Janet Taylor's contribution in the compass adjusting controversy ...
    While the effects of magnetic variation and deviation on compasses were well known by 1800, iron ships brought with them an even bigger challenge. The nautical ...
  78. [78]
    NGA, NOAA, BGS Release World Magnetic Model 2025
    Dec 17, 2024 · The WMM is a joint product of NGA and DGC. The model and associated software are jointly developed and distributed on behalf of NGA and DGC by the NOAA ...
  79. [79]
    Magnetic Variation | SKYbrary Aviation Safety
    Magnetic variation, also called declination, is the angle between true north and magnetic north, which varies with position and time.
  80. [80]
    [PDF] 160422 PARC MagVar VOR Recommendations
    Apr 22, 2016 · The PARC recommends increasing the VOR magnetic variation tolerance from the current 3 degrees to 5 degrees.
  81. [81]
    [PDF] Aeronautical Chart Users' Guide
    Feb 20, 2025 · Isogonic Line and Value. Isogonic lines and values shall be based on the five year epoch magnetic variation model. Local Magnetic Notes.
  82. [82]
    [PDF] Chapter 8 (Flight Instruments) - Federal Aviation Administration
    The flux gate compass that drives slaved gyros uses the characteristic of ... Only AMTs can adjust the compass or complete the compass correction card.
  83. [83]
    Grid Navigation | SKYbrary Aviation Safety
    Proximity of the magnetic poles - large and rapid changes in variation make magnetic compasses unreliable, even over relatively short distance; Ground based ...
  84. [84]
    High Latitude Operations - Code 7700
    Dec 30, 2020 · Within these areas, air navigation tasks are further complicated by very rapid changes in magnetic variation over small distances.
  85. [85]
    [PDF] ICAO True North Advisory Group (TRUE-AG) - Update - IFATCA
    Apr 28, 2025 · In-person for 2025 are planned for 3-7 March and 8-12 September. 2.2. Global transition and switch to true north as reference for the global ...
  86. [86]
    [PDF] FOURTEENTH AIR NAVIGATION CONFERENCE - ICAO
    6) Ongoing work on the change from magnetic to True North. 7) Ongoing work concerning an update to the Global Air Traffic Management Operational Concept. (Doc ...