Based on Calibre 899, Calibre 923 incorporates many changes. Most obvious is the world timer mechanism, which functions more as a dual timezone readout than a true worldtimer since only a few timezones are visible at once. Also different is a uni-directional winding mechanism similar to the "Autotractor", which is more efficient, with ceramic bearings. A larger barrel provides 45 hours of power reserve, and the mechanism is more efficient thanks to re-contoured gears. Additionally, fine adjustment can be made with four regulator screws.