The 2500 is based on the Omega 1120 calibre, which was itself a derivative of the popular ETA 2892-A2. This calibre was the first ever to include the Co-Axial escapement invented by George Daniels on its introduction in 1999. The movement comes in versions 2500A, 2500B and 2500C.
Calibre 2402 is a skeletonized no-date version of Cal. 2500.
Calibre 2403 is a no-date version of Cal. 2500.
Calibre 2507 is a no-date version of Cal. 2500 with “bullet” decorations on the rotor.
Calibre 2628 is a version of Cal. 2500 with an adjustable central 24 hour hand.