1940's Tissot Wristwatch

[Clochemerle]

I am looking at a friend's 1940's Tissot wristwatch. The watch runs well and keeps good time when worn and when laid in any position other than flat on it's back when it will gain 30 mins in 12 hrs. I can't see what is causing this. Does anybody have any ideas please.

Regards, Andy.

[Marc]

Have a look at the balance spring and see how close it comes to the balance cock.

When the watch is sitting face up or flat on its back the balance spring will sag slightly towards the balance cock.

If the spring isn't true in the flat and parallel to the balance, or if the collet isn't properly seated, then when the watch is face up the hair spring can come into contact with the cock, effectively shortening it and causing the rate to increase.

[Clochemerle]

Thanks Marc, I'll look at that.

[Clochemerle]

Yes that was it. All fixed now. Many thanks Marc.

[Marc]

Excellent :-)