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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




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