The pusher at 10 moves the yellow arrow countdown hand in one minute increments up to 10 minutes. Once the countdown hand is set, the pusher at 2 starts the yellow-tipped seconds hand moving COUNTERCLOCKWISE until the countdown is complete. Then, it automatically reverses itself and moves CLOCKWISE acting like a regular chronograph.
If the countdown hand is not engaged, the chronograph functions like a normal chronograph with the initial push on the pusher at 2.
I'll try to link a video.