It took some research to find this in old Heuer catalogues, but we succeeded!. The reference number is and it was found in the 1976 catalogue (Thank you: on_the_dash!). It is a rare stop-watch, used for doctors and athletes to control the pulsbeat. The numerous scales traces some figuring out, but you can time your puls beats during time lapses of 10 or 30 seconds. The dimensions are: diameter 53 mm and thickness 19,5 mm.