NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Manual calculation of compass variation
From: Herbert Prinz
Date: 2004 Oct 17, 01:01 -0400
From: Herbert Prinz
Date: 2004 Oct 17, 01:01 -0400
Borda reports (Verdun de la Crenne, Borda, Voyage fait par ordre du Roy en 1771 et 1772) that the biggest effect on compass deviation is caused by the guns. The Endeavour apparently had some 20, I didn't check Cook's other ships. When possible, observations for variation were also taken on land with a chance of better accuracy. For a land observation, I don't find a specification of minutes unreasonable. On a compass rose of 15cm diameter one can easily read 1/4 degrees, so that an average of 3 measurements would result in a nominal accuracy of 5'. At least, this was the reasoning. Herbert Prinz