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I own a postage envelope stamped on the South Pole (?) and devoted to Zenith Pilot watches cal. 5011. Does anyone have any info on such envelopes? Who, when, where, why, in what way, by what means, how much?

I own a postage envelope stamped on the South Pole (?) and devoted to Zenith Pilot watches cal. 5011. Does anyone have any info on such envelopes? Who, when, where, why, in what way, by what means, how much?

The only difference between my books is shown with the red arrow

Three editions at least. I have two of them.

Until 1925 not only the precision of a movement allowed to get a Chronomtre exam by the observatories. It also must have a physical chronometre construction of the escapement. The producers of high precise movements revolted against it and created the therm "1/2 chronometre". It should say: It is pr

I have a Georges Favre-Jacot pocket 1/2 Chronometre (cal. Billodes 19'''-54, 23 jewels, silver case) that was made for the old Russian market. Does anybody know another Zenith/G.F.J/Billodes half-chronometres? I didn't find such type of watches in Manfred Rössler and Joël Duval books.