I purchased a Thomas Mercer Chronometer #21685 at an auction last week. It appeared in excellent condition, fully wound but not running. After reading Marvin Whitney's "The Ships Chronometer" I was able to remove the movement from the brass bowl. Removing the balance cork(a folded piece of paper) started the movement. It is keeping very good time. My question is how much wind should I leave on the mainspring when I stop the balance wheel again and cork it for storing the chronometer. A lable in the box indicates that it was seviced in April 1977 in Cape Town( I assume South Africa). This is my first Chronometer and I don't want to cause any damage. If any one has the Mercer Chronometer book could you look up the date of manufacture of #21685? I think this is a 1960"s chronometer. Thank you in advance. Scott

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Hello Scott,

Your Mercer marine chronometer with s/n 21685
was made around mid 1956.

Mun C.W.

I have six marine chronometers, including a Mercer. I don't leave any power on the mainspring, and have never had a problem. I wind them about once every other year. I don't cork them since they are not going to be subject to any violent movement.

Thank you Mun and Jerry.

Scott

Scott, after corking, you should wind the chronometer just enough to move the wind indicator a little. Refer back to Whitney, p. 64, where he says never leave a chronometer without some wind on it, as it may damage the locking jewel if the chronometer is not properly handled. He says that happened to early Hamilton chronometers, so the jewel and some other parts on those were redesigned to lessen the chance of damage.

If the chronometer isn't moved, nothing will happen to it, but can you guarantee it won't be jostled while it's stored?

The three chronometers I don't wind are corked and have just a bit of wind. That way, I can handle them if I want without any worries.

Interesting that a 1956 Mercer still has what appears to be an Earnshaw expansion balance. Wonder what the hairspring is made of?

Norman

Norman: I referred to Tony Mercer's 2003 book titled Mercer Chronometers. The book indicates that after 1935, Mercer used hairsprings made from an alloy of Palladium. As for balances, it appears they continued to used plain bi-metallic compensation balances. This is odd, considering that Thomas Mercer had deveoped and used a balance with auxilliary compensataion of his own. It does not seem to have been used on every Mercer made. Unlike the Americans who used exotic alloys for balances and hairsprings, the very conservative English manufacturers stuck to the old ways.

Jerry Freedman