Coin watch
From Infogalactic: the planetary knowledge core
A coin watch comprises a watch inserted into a coin or medal.[1]
A coin watch is typically made by slicing a coin into two disks, one thinner than the other;[1] or by removing one face of a coin. A watch is then embedded into the thicker part, and the two faces joined by a concealed hinge and catch.[1] When closed, the watch is hidden and the coin looks like any other.[1]
Noted makers of coin watches include Cartier[1][2] and Corum.
References
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