Royal Oak Chronograph REF. 25860ST.OO.1110ST.04

The first Royal Oak Chronograph ref. 25860 was launched in 1998 equipped with calibre 2385, an automatic chronograph movement based off of the legendary Frederic Piguet calibre 1185 also used on the Vacheron Constantin Overseas Chronograph —as caliber 1137— and the Breguet Marine Chronograph —as calibre 576— amongst other timepieces.
This movement still remains the thinnest automatic chronograph calibre ever made, measuring only 5.5mm in thickness.
The movement is composed of 304 parts, beats at 21,600 vph, is fitted with 37 jewels and provides a power reserve of 40 hours when fully wound.