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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude by compass variation
From: David Pike
Date: 2025 Jun 3, 14:59 -0700
From: David Pike
Date: 2025 Jun 3, 14:59 -0700
Those with time to do some simple checks will find this chart useful.
https://www.ngdc.noaa.gov/geomag/WMM/data/WMM2020/WMM2020_D_BoZ_MILL.pdf
Around 60S 15E would be a good place because in 2020 you got 12° chVar per 15°chlong. If you can mange to measure Var to 1/2° you might be able to calculate long with an accuracy around +-30'(30nm), about the same as my astro. Near me at 53N 000E/W, its 6°chVar per 15°chlong, so perhaps an accuracy of +-1.5°long(90nm). Don't foget there's also a diurnal change in variation as well as the ever moving anual one. Years ago, when we did air swings, we used to be able to get this from the Admiraty Compass Observatory, but times and places change. DaveP
