From a bit of digging I believe it may be the Heuer Calibre 1666, which is then an A.Schild movement originally.
You can see a picture of the movement in this linked PDF:
https://www.cousinsuk.com/PDF/categories/3220_Heuer 736,1564,1666 Page 1.pdf
The Valjoux movements seem to have been introduced in the late 60’s, whether this was for all models or not I am not sure, but certainly for the Monte Carlo and I assume any other 1/100 stopwatches. A quick google of Heuer Monte Carlo and you should find the same movement as yours.