Thank you for the invitation
@Vitezi! Yes, I think I can offer a bit. I agree with JimInOz’s comments, very good.
This is a 19’’’CHRO, the first of Omega’s chronographs, originally dating from 1898 - and because of this dating, I’d expect the movement to be a 19’’’ CHRO HNB.
The case will be listed as ‘Acier’ - which is French for steel, but in those days not stainless steel: it would be mild steel and possibly with a gun metal finish. The case looks original (Omega) to me: we see the inner case-back/dustcover - I think the outer case-back will have the Omega mark on the inside.
I agree with Jim that the case number dates it at around 1904. The movement number will of course be under the dial.
The minute track on the dial is marked to 1/5th second - which is why it is marked up to 300. Of significance is that there are two sub-dials - continuous seconds at 6 o’clock and at 12 o’clock is a 30 minute counter. Later dials on the 19’’’CHRO were the ‘special A.T.’ dial with the ‘CADRAN BREVETE S.G.D.G.’ - which (typically) did not have a sub-dial at 6 o’clock and the sub-dial at 12 o’clock was a 15 minute counter.
Jim is correct in noting the ‘M’ on the movement (to which
@Tire-comedon has previously referred), which was used on watches destined for France. ‘M’ was used if the movement was cased in metal, ‘A’ (for Argent) if the case was silver and ‘O’ (for Or) if the case was gold.
My own version in gun metal, quite similar to the OP’s, is below. This came from another distinguished OF member!
Lovely watches - and now over 120 years old!