The movement is Piaget’s in-house caliber 883P. This is a hand-wound, column wheel, flyback chronograph without date. It’s column wheel controlled, with vertical clutch coupling, and it is 12 lignes/27 mm in diameter, under 5 mm thick at 4.65 mm. It’s got a 50-hour power reserve, and runs at a frequency of 28,800 vph. Basically this looks to be the Piaget 880P caliber but minus the date and the rotor and automatic winding train; 880P for comparison is 5.6 mm thick (which gives you an idea how thin the sub-assemblies for both actually are).  This is, by the way, also a dual time chronograph; the register at 9:00 is a 24 hour hand, showing a second time zone.