The Zenith watch company, founded by Favre-Jacob has been producing fine watches since 1899, and production of fine wrist watches steadily grew though out the 20th Century. They are know for one of the first automatic/date chronograph movements produced in the early 1970’s. A well researched article about the company can be found on the Hodinkee website.
This fine gold wrist watch came in for service and a new mainspring. Simple and well designed it ran well after cleaning an oiling.