Hansord Antiques has dated this piece to the Victorian era.
It is listed as having a non magnetic white metal balance and spring, and a rare non-ferrous detent.

It was serving on a number of ships from 1895 until 1948 including (full list available):
HMS Jupiter
HMS Effingham
It then became part of the Blackwell collection in the USA and was sold on his behalf by David Penny
12cm Dial diameter
Hansord Antiques has dated this piece to the Victorian era.
Furniture, works of art,globes ,and scientific instruments
You can view the stock and full dealer information on the Hansord Antiques Profile Page
Hansord Antiques is a registered member of LAPADA BADA CINOA