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This is an interesting question.

If you know your latitude and longitude, then you can fit your chronometer to 
the known altitude.  If the altitude is wrong for the time, then you can 
adjust the chronometer error as a function of the longitude you find.  A 
lunar observation can be solved, with a known position, to adjust the 
chronometer error.  In fact, for a known position, many different 
observations can be used.  The only requirement is that time is parameter 
when solving for a known position.

Apparent time at sea may be found by Von Littrow, Bowditch and others, but I 
do not believe this recovers GMT or UT.

But your question is, I think, recovering time when at sea, using only 
chronometers.  I have read about expeditions that kept as many as 22 
chronometers, when on survey expeditions (the name escapes me).  In this 
circumstance, voting will permit the accurate recovery.

Best Regards
Brad



-----Original Message-----
From: NavList@navlist.net [mailto:NavList@navlist.net] On Behalf Of Greg Rudzinski
Sent: Wednesday, May 06, 2009 1:11 PM
To: NavList
Subject: [NavList 8157] How Many Chronometers?


     When a time tick or other master reference is not available then
by what means can a navigator at sea use to determine whether a
chronometer is maintaining a consistent rate. If two chronometers are
carried then an inconsistency between the two would suggest a problem
but then which chronometer is at fault? How about a third chronometer
to help the navigator determine which chronometer is behaving badly.
Carrying three chronometers does triple the chances of one going down
but since quartz watches are cheap why not carry three?

Greg


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