Ron_W
1636
Congrats on this really nice condition Heuer ! From what i read on Onthe Dash and Omegaforum the number on the back , such as 70 /112, designates year of production and number of watches.
While there were very few made, it does suggests more than 100 pieces in said year i think. But the one such as in your condition is probably a less than 10 pieces survivor. So real treasure