NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Compass Checks at Sea
From: Greg R_
Date: 2008 May 22, 21:26 -0700
From: Greg R_
Date: 2008 May 22, 21:26 -0700
--- Billwrote: > I have thought for many decades that question might be cannon fodder > for a Monty Python "Confuse a Cat" skit ;-) (A UK comedy show > beloved in the colonies in my youth.) Tell me sir, have you confused your cat lately? You can tell me, I'm a navigator... ;-) > The instructions for a bushwacker (land) compass will refer to the > difference between true and magnetic "declination." And just to confuse the issue even further, both land and sea (airplane) pilots refer to compass error as "deviation" (at least in the USA, don't know if that's universal throughout the aviation world or not). -- GregR > > Greg R wrote >> >> Perhaps you mean "deviation", or is that called "declination" (i.e. >> the error of the compass itself, usually related to the >> surroundings in which it's mounted) in other places of the world? > > I have thought for many decades that question might be cannon fodder > for a Monty Python "Confuse a Cat" skit ;-) (A UK comedy show > beloved in the colonies in my youth.) > > For USA sailors, deviation is the difference between what a magnetic > compass reads and what it should read magnetically without external > influence. Hence a deviation card for various headings to correct the > reading to actual magnetic. Variation being the difference between > magnetic and true at any given location on earth. > > The instructions for a bushwacker (land) compass will refer to the > difference between true and magnetic "declination." > > Easy to confuse for me. > > As a sanity check I always go back to the conversion from compass to > true: > Can dead men vote twice at elections? CDMVTAE. (The answer in > Chicago, IL, USA is, "yes.") > > C is compass reading > D is deviation (added or subtracted to the compass reading) > M is is magnetic after adjusting for deviation > V is variation (to be added or subtracted to magnetic for true) > T is true > > A (add) > E (East) Add east variation, subtract west variation. > > That helps to keep what deviation is straight in my mind, as well as > differentiating it from land declination (variation to me). > > Bill B > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---