Valjoux Cal. 84 is a column wheel chronograph movement. It features a six-column wheel controlling the chronograph function and has two pushers and a 30 minute chronograph register. It was exclusively produced for Bovet Frères for their “Mono Rattrapante” between about 1936 and 1950.
This is a “lépine” pocketwatch movement, with the small seconds placed on the same axis as the winding crown. In a pocketwatch, this would place the small seconds at 6:00 with the winding crown at 12:00. The image above would show its placement in a wristwatch, with the winding crown at 3:00 and the small seconds at 9:00.