Cal. 103 CHR was the first chronograph movement produced by Vénus. Introduced in 1933, it was based on their 10.5 ligne round movement family, which began with Cal. 75 and was widely produced in the 1920s and 1930s. It is a monopusher movement with a running central chronograph hand and no stop or counter mechanism.
Cal. 103 CHR is unusual in many ways. It has no counters or start function, with a continuously-running central chronograph hand reset on demand using the pusher. It was conceived without the conventional column wheel, relying instead on simple cams to reset the running seconds hand. The pusher was co-axial with the crown. A similar mechanism was used on Cal. 131 CHR, a tonneau-shaped movement produced later in the 1930s.
Later iterations of a chronograph on Cal. 103 appear quite different, with a column wheel and separate pusher at 4:00. It is likely that these, although still called Cal. 103 CHR, are a completely different design.
More detail on the history of Vénus is available in the Grail Watch article, “The Rise of Vénus, Legendary Chronograph Maker“