And rebuild they did, as the RD#5 features the brand-new self-winding Calibre 8100, with a radically different architecture to any chronograph movement seen before, all in a compact package of 31.4mm by 4mm. Its most significant change comes in the reimagining of the chronograph zero-reset system, replacing the conventional hammer-and-heart-cam design with a rack-and-pinion system. Each chronograph hand is tied to a particular rack, and when the chronograph runs, the racks store the energy that typically would be lost through friction in a normal caliber.
For example, when the chronograph’s seconds hand completes a full revolution, the rack disengages with its pinion, releasing the stored energy (like a rubber band) and then starts over again to propel the hand forward. Simultaneously, the stored energy is used to increment the minute counter forward, which is geared to and also drives the hour counter.