Audemars Piguet added a chronograph to the Royal Oak in 1997, the design's twenty-fifth anniversary. Reference 25860ST kept the disciplined 39 mm footprint of the original family but introduced three registers and rectangular pushers without breaking the case-and-bracelet flow. Its compact proportions and Frédéric Piguet-based caliber 2385 make the first generation distinct from today's larger watches.
The 26300 refined the 39 mm format before the collection moved to 41 mm with reference 26320 in 2012. The larger dial created more breathing room, while colour combinations and contrasting “panda” registers became a major part of the model's identity. Reference 26331 marked the chronograph's twentieth anniversary in 2017 with broader subdials and revised details, still using the slim, proven caliber 2385.
Reference 26240 brought the decisive mechanical change in 2021. Its in-house caliber 4401 adds a flyback function, column wheel and vertical clutch, and the sapphire back exposes a movement designed for the case rather than adapted to it. Earlier references offer slimmer proportions; the current generation provides newer architecture and a more assertive presence. For any pre-owned example, cycle start, stop, reset and flyback functions repeatedly, check that every hand returns exactly to zero, and examine the bezel, pusher edges and bracelet for heavy refinishing. Dial and hand combinations should be verified against the full reference suffix, not only the six-digit family number.
