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Hi Jim

Your definitions are precise.

Chronometer rate is the gain or loss of time per day, or whatever period you 
may chose to define.  The assumption is that the rate is constant is 
fallicious.  The rate of a chronometer varies with many factors.  Take a 
close look at the chart recently provided by George.  

If the rate was constant, the line would be straight, independent of 
corrections at known longitudes.  In fact, we see the converse.  The line 
changes slope from correction to correction.  We even see positive going 
slopes change into negative going slopes.  The rate, therefore, is changing.  


The argument will be offered that modern mechanical chronometers are superior. 
 In fact, they are.  However, they are not perfect.  The rate still changes 
with the viscosity of the lubricant with temperature. Hence the double box, 
to slow the transfer of thermal energy, with a glass top, such that you can 
see the chronometer without opening the box. The quartermaster is cautioned 
to wind the chronometer every day, at the same time, by the same amount, such 
that the chronometer utilizes the same spring region, independent of the wind 
down counter that provides the hours until unwound.  All this attention to 
detail, and the rate still varies.

If you remember other parts of the Royal Observatory, where H1 lives 
(hooray!), then you have seen the gradual transformation to other time 
pieces, away from the mechanical.  And each time piece has been superceded by 
the next, each with dilemmas, problems and issues.

Back to Greg's question though, which I understand to be the determination of 
when a chronometer has gone bad, we have offered the solution of solving for 
time when the longitude is known. If the longitude is not known, then you 
suffer from not knowing which one is wrong, the longitude or the chronometer! 


Bruce Stark, when he was contributing to the list, offered a wonderful 
exposition on how to recover GMT via lunars.  The details are found in a 
NavList posting whose number I cannot remember.  I did keep a file of it 
though, and link it herein.  All the way from not knowing any time to GMT! I 
have not exercised the method and can offer no insight as to how accurately 
one can recover GMT from it.  Based upon the source, however, I suspect it 
works quite well!

Best Regards
Brad 

File: 
Recovering-GMT.doc



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