The other day I described the “slow twitch” way of purchasing a watch. On the other end of the spectrum is the “fast twitch” mode of operating. Having a quick trigger is relatively easy with new watches. You have a good idea what quality you will receive. The watch will tell time, it is just a matter of whether you will get excited about it. (You have my blessing to buy a Bulova or Citizen on Prime Day: use the fast twitch.)
With vintage watches having a fast twitch is a real gamble. The watch that you receive may be just a “watch-like” substance, incapable of keeping time and destined for a drawer. In an online auction you only have the seller’s pictures, a limited idea about their reputation, and whatever knowledge about the watch that you can glean from the internet.

Would you have taken a flyer on this? The crystal had taken years of abuse. It doesn’t have a strap, which means that it has sat unloved and unworn for many years. It is a brand that is little known.

I have a theory, admittedly based upon a small sample size, that a high percentage of watches are retired from active service due to cloudy acrylic crystals, not any performance issues. We have been moving away from the cobbler and watchmaker for generations. Many things that could be repaired are merely replaced.
Well, I took the fast twitch gamble. This seller had a 100% rating with over 10k transactions. This tells me that I risk very little. The seller wants me to be satisfied. They primarily sell other goods, so they will not overvalue a watch. What will a little Polywatch do?

A little soapy water will remove the traces of the wearers before me.

LeMarc is a brand of Marc Nicolet & Cie of La Chaux-de-Fonds. The Nicolet family has long roots in the watch producing region of Tramelan. I can’t tease out exactly which branch of the family this is, but they are still active in the watch industry. I would guess that this is a mid-1960’s example.

Unlike a screw back, I can’t easily take the back off, as is helpfully noted, to see what movement is contained therein. So, this is a front loader and beyond what I can do safely. Once it cleaned up I noted some paint loss on the outer rim of the dial. Some watchmaker had some difficulty too is seems.

I think that it is good enough to wear. Not perfect, not showroom quality, just good enough for the vintage collector who can accept imperfections. I will eventually take it to the watchmaker and maybe the dial can be cleaned gently and see what movement I have.. It has been within a minute in the last 24 hours, not bad for a fast twitch gamble.
Addendum:

Housing an ETA 2451. A good bet.