Thanks friend.. I try find some information about this letter M on mainplate.. I find this Cort on ebay, never see before 616 in this case.. I order new mainspring.. Next is make service, short second pinion.. Question is polish maiplate or not?

looks so nice with the 616 insideNortON wrote:
Laer wrote: ↑May 1st, 2024, 5:50 am I picked up an interesting pocket watch today at a local antique market.
At first glance, it looks like a Cortebert cal. 616, but behind the balance I see the UNITAS markings and the numbers 285 and 497.
Does anyone know anything about this movement?
Unitas 285 497 ?
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