Finchingfield Antiques has dated this Thomas Mercer Marine Chronometer to the 1940s.
Both the inner and outer boxes are in very good condition. The travel case has a leather strap with buckle.

I has the number 17989 which we believe dates the clock to 1947.
The silvered dial has a very unusual cut out where the seconds wheel can be seen as it steps out the seconds.
The nicely blued hands are also in very good condition.
Finchingfield Antiques has dated this Thomas Mercer Marine Chronometer to the 1940s.
You can view the stock and full dealer information on the Finchingfield Antiques Profile Page