I bought this a couple weeks ago.

Charles Frodsham Detent Chronometer, It has a broken staff. 48mm

Here's the movement.

It is free sprung.

Looks very nice and is of good quality and interest. Seeing your post reminded me that I'd previously meant to find out about 'AD Fmsz' but hadn't got round to it. Originally a code for 1850, it was apparently then adopted as a sort of 'logo' to signify superior quality. By the number, this movement should date from the late 1860s.

I hope you'll be able to have it running without too much trouble and I'm sure you'll derive much pleasure from its ownership.

I've looking for a case that this will fit.