Editing Magnetic declination (section)

=== Models and software ===
{{see also|Earth's magnetic field#Statistical models}}
Worldwide [[empirical model]] of the deep flows described above are available for describing and predicting features of the Earth's magnetic field, including the magnetic declination for any given location at any time in a given timespan. One such model is [[World Magnetic Model]] (WMM) of the US and UK. It is built with all the information available to the map-makers at the start of the five-year period it is prepared for. It reflects a highly predictable rate of change,{{efn|This rate of change is known as the [[geomagnetic secular variation]], and current models using a constant variation over five-year periods are on average ([[root mean square]]) off by 15 arcminutes at the end of each forecast.<ref>{{cite journal |last1=Fournier |first1=Alexandre |last2=Aubert |first2=Julien |last3=Lesur |first3=Vincent |last4=Thébault |first4=Erwan |title=Physics-based secular variation candidate models for the IGRF |journal=Earth, Planets and Space |date=December 2021 |volume=73 |issue=1 |pages=190 |doi=10.1186/s40623-021-01507-z|bibcode=2021EP&S...73..190F |s2cid=239022300 |doi-access=free }}</ref>}} and is usually more accurate than a map—which is likely months or years out of date.{{citation needed|date=February 2014}} For historical data, the IGRF and GUFM models may be used. Tools for using such models include:

* Web apps hosted by the [[National Geophysical Data Center]], a division of the [[National Oceanic and Atmospheric Administration]] of the United States.<ref>{{cite web|work=Geomagnetism |url=https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml |title=Estimated Value of Magnetic Declination |publisher=NOAA National Geophysical Data Center |access-date=6 December 2013}}</ref>
* C demo program that for WMM by the [[National Geospatial-Intelligence Agency]], along with various other third-party implementations.<ref>{{cite web |last1=Meyer |first1=Brian |title=World Magnetic Model - Software Download |url=https://www.ncei.noaa.gov/products/world-magnetic-model |website=www.ngdc.noaa.gov|date=8 February 2022 }}</ref>

The WMM, IGRF, and GUFM models only describe the magnetic field as emitted at the core-mantle boundary. In practice, the magnetic field is also distorted by the Earth crust, the distortion being [[magnetic anomaly]]. For more precise estimates, a larger crust-aware model such as the [[Enhanced Magnetic Model]] may be used. (See cited page for a comparison of declination contours.)<ref>{{cite web |last1=National Centers for Environmental Information (NCEI) |title=Enhanced Magnetic Model (EMM) |url=https://www.ncei.noaa.gov/products/enhanced-magnetic-model |website=www.ngdc.noaa.gov |date=10 March 2022 |language=EN-US}}</ref>