There are many forms of Heuer Yacht Timers. This one, with the loop for a neck string/band can be dated to ca 1965. It is fully functional and has dimensions: diameter 52,5 mm and thickness 17,3 mm. The label on the back is too worn unfortunately, so the exact reference number is difficult to be certain about. Look at the attached catalogue copy that we have onthedash.com to thank for a similar version.