Re: [TR] Quest

["David Brister" <david.brister@wanadoo.fr>]

 If one were super pedantic, one would point out that Variation is the 
difference between True North and Magnetic North which is very exactly 
determined worldwide by the geological surveying people and marked on maps 
and charts with a date and accompanying information about the the annual 
change of Variation for that epoch as they call it. This exists as the same 
value at any place regardless of the compass being used. Also in high 
latitudes the angle of Dip (be quiet that dirty minded boy at the back) 
becomes significant.
The thing you have to deal with  concerning your TR compass is Deviation 
which is the difference on any given heading between magnetic North and your 
compass reading. This is local to your car and the value which must be 
determined round the compass so that it can be applied to the compass 
reading to give a magnetic heading.
Randall is quite right to suggest that compass deviation will vary with 
every change of electrical current flow but in purely practical terms the 
first first two paras here and Randall himself are  theoretical as far as a 
car compass is concerned unless you are in the North of Alaska or perhaps in 
the Antarctic where Variation becomes extreme.
Practically I have found that a decent quality floating ball compass fixed 
at the top of the windscreen of an open car normally is within 10 or 15 
degrees of the magnetic heading. However if you watch your compass when you 
are braking or accelerating you will find it swing quite wildly. Probably 
better to watch the road.
Which direction did that man say the sun rose from? Lets get back to the 
chain tensioner discussion.

David Brister
1967 TR4A


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