This is a stainless steel Audemars Piguet Royal Oak Chronograph, 25860ST.OO.1110ST.03. It has an integral stainless steel bracelet with a double deployant clasp, and a scratch resistant sapphire crystal. There are two round pushbuttons for the chronograph. The 40mm diameter solid three-body case, bracelet, and distinctive octagonal bezel with 8 hexagonal blued screws are brushed/polished. It has a screwed down winding crown, and the solid case back is secured with 8 gold screws. The dial is black with Clous-de-Paris tapestry "waffle" texture, luminous dot and baton indexes, luminous white baton hands, and a luminous white center chronograph hand. There is a subsidiary dials for the small seconds at the 6 o'clock position, a 12-hour register at 9 o'clock, and a 30-minute sub dial at 3. The aperture window for the date is between 4 and 5 o'clock. It's water resistant to 50 meters/165 feet, and it has a power reserve of 40 hours at full wind. The 11mm thick case, dial, and movement are all signed. The automatic self-winding Audemars Piguet caliber 2385 movement is rhodium plated, with oeil de perdrix decoration. It's constructed with 37 jewels, a shock absorber mechanism, and a straight-line lever escapement. It includes a monometallic balance adjusted for heat, cold isochronism and 5 positions, a self-compensating flat balance spring, and a 21K gold rotor. The mechanism oscillates at a frequency of 21,600 vph (3Hz). Audemars Piguet produced the first Royal Oak in 1972, with a custom Jaeger LeCoultre movement designed by the brilliant horologist Gerald Genta. It was named for the British battleships of World War II, which in turn were named for the oak tree in which Charles II of England hid from his enemies, the Roundheads.