This is a stainless steel Audemars Piguet Royal Oak Chronograph, 26320st.OO.1220ST.01. It has an integral stainless steel link bracelet with a double deployant clasp, and a scratch resistant anti-reflective sapphire crystal. The 41mm diameter solid three-body case, bracelet, and octagonal bezel are brushed. The solid case back and bezel are each secured with 8 hexagonal screws. It has screwed down chronograph pushbuttons and a screwed down uni-directional winding crown. The dial is black with a grande tapestrie "waffle" pattern, with applied white gold baton hour markers with luminescent fill, luminous white gold baton hands, and an outer minute track. There is a date aperture between 4 and 5 o'clock, a small seconds sub dial at 6 o'clock, a 12-hour register at 9 o'clock, and a 30-minute dial at 3. It's water resistant to 50 meters/165 feet, and there is a 40-hour power reserve at full wind. The 10.8mm thick case, dial, and movement are all signed. The automatic self-winding Audemars Piguet caliber 2385 movement is rhodium-plated, with fausses cotes embellishment. It's constructed with 37 jewels, 304 components, and a shock absorber mechanism. It includes a straight-line lever escapement, a monometallic balance adjusted to heat, cold, isochronism and 5 positions, a self-compensating flat balance spring, and an 18K gold rotor segment. It has an 18K gold oscillating weight, and the balance wheel turns at a frequency of 21,600 vph (3 Hz). 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.