That's a really tough one, for a number of reasons.

In fact, I can't give you a very precise answer for either year or model, but let's run through a few thoughts and see where we end up.

- The "Heuer" shield on the dial is shallow compared to later watches, which says early. As in the 1940s or earlier.

- Then we look at the case and get an even earlier impression. That single pusher within the crown usually signifies that the movement originally came from a pocket chronograph rather than a wristwatch version. On the pocket watch, the crown will typically be at 12 o'clock so the dial is refinished and rotated and fitted, along with the movement, into a new case with lugs so a strap can be attached.

- Now, those pocket chronographs are normally considerably larger than usual for a wristwatch, especially bearing in mind that watches of the 20s and 30s would be considered small in comparison to many of today's watches. I can't get much sense of scale from the photo but that doesn't seem to be so here? I'm minded to think that this was a Heuer wristwatch dial and movement that has been recased in that gold case, which was perhaps an heirloom. Of course, if you come back and say it is big, then I just fall back on the recased pocket watch theory!

- A recase in this period isn't something to particularly worry about. Wristwatches started to gain some use for convenience during WWI and rapidly became more popular than pocket watches by the start of the 20s. Demand was ahead of supply, but there were plenty of pocket watches around and a talented watchmaker was readily able to convert one into the other.

- Let's go back to that dial. One of the reasons I think your watch might be converted from a wristwatch is the similarity of that dial to that of a model 349, as per the one below, shown in a catalogue from 1938:

The registers look similar to that watch, but the numbers are subtly different. More like this same model in 1945 in fact:

So that gives us a broad time frame for the dial, albeit it could also be from earlier, perhaps as early as the 20s. I'd normally want to be much more accurate than a ~25 year range in dating a watch but I'm not sure I can be here. The hands look correct for the period.

- That leaves one lingering question in my mind. If you look at both catalogues, the watch has two pushers in each, one to stop and start the chronograph, the other to reset it to 0. Your watch has the single pusher to perform all 3 functions. It's not beyond the scope of a very talented watchmaker to amend the movement, but it's certainly no mean feat. A shot of the movement in close up would be really helpful if you have one, but don't go about opening it up to look unless you're comfortable doing so.

So my conclusion would be a recased watch from somewhere around the 20s to immediate post-WWII, using some components from what appears to be a 349 mated to a custom case. Our information, and my knowledge, on that era is a bit sketchy compared to later though and I could be wrong in some or all details. It could be the first appearance of what would become the 349 in a sort of transitional case midway between pocket- and wristwatch, in which instance it would date from before 1938, the earliest catalogue over on OTD.

So sorry not to be definitive on what your watch is, but it's certainly interesting and intriguing!