Valjoux Cal. 20 is a pocket watch column wheel chronograph movement. Introduced around 1910, it was produced at least through the 1920s. It featured a six-column wheel to control the chronograph function. The chronograph used a central seconds hand with split seconds and a 30 minute counter. It was a dual-pusher design.
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.