
Inspired by historic triggers of various types, what you have is a unique system which builds on the base Swiss ETA Valjoux 7750 automatic chronograph movement architecture. The trigger is used to start and stop the chronograph via a button that is actually in the crown (similar to many monopusher chronographs), and a separate pusher above it is used to reset the mechanism.
Graham caliber G1733 (as they call their version of the modified movement) is an automatic operating at 4Hz with 48 hours of power reserve. Complications include the time, big date indicator, GMT hand, and 30-minute chronograph.