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A question was asked on the other list by Red about mechanical chronometers. I 
can stop by and read the list but am unwilling to join so I can not post to 
that list. I have an interest in chronometers and collect them so I wanted to 
speak to that question while I have the chance.

You asked about what makes a ships chronometer a chronometer. A chronometer is 
not always a great time keeper but it is instead a constant time keeper. The 
rate or error is always the same so that you can correct the reading of the 
dial to get GMT.

They differ in construction from a watch or clock. The common configuration, 
and that is of both the Hamilton and the MMX is to have a chain drive with a 
set of steps in it so that the power from the main spring is transferred 
evenly as the spring winds down. The steps change the leverage of the drum as 
the chain winds from one drum to the other. The steps are arranged in two 
pyramids with the small end of one at the large end of the other. You also 
have a maintaining spring in addition to the main spring. It keeps the works 
running while you are winding it. The balance wheel is poised in the face up 
position and is biased to temperature compensation because the gimbals keep 
it in a face up position. A railroad watch on the other hand is poised in 
more positions but is not as well compensated for temperature. It was 
intended to stay in the conductors pocket and stay at an even temperature. 
You can poise a balance wheel for one or the other but not both. You can not 
regulate !
 a chronometer in the way you can a watch or clock. The balance weights need 
to be adjusted and that affects poise so it is very difficult to do with out 
the service tools.

I have a MMX and the gold plated movement is beautiful to see but my Hamilton 
is a much better chronometer and has a lot of features that the MMX does not 
have. I have the original service book for the Hamilton and it describes the 
design and unique features of that design in great detail. I can copy parts 
of it if you need some information. My documentation on the MMX is not in 
English needless to say and I have no idea what it says.
Robert Gainer

   

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