1973 Zenith Diver World timer ref. A3634, a hard to find watch, 38mm. case, cal. 2552PC.

Zenith is a luxury Swiss watch manufacturer founded in 1865 by Georges Favre-Jacot at the age of 22. Zenith was purchased by LVMH in November 1999, becoming one of several brands in their watch and jewellery division.
Zenith has a long reputation for the quality and precision of their watches. It is one of the few Swiss watch manufacturers that still produces their own movements in-house, including the Zenith el Primero – one of the first automatic chronograph movements from 1969.