Oris Aquis depth gauge dive watch

Oris Aquis depth gauge dive watch with mechanical depth gauge. Is the “first divers watch which measures depth by allowing water to enter the timepiece.”

Oris Aquis depth gauge functions by applying the Boyle Mariotte Law (aka Boyle’s Law): the absolute pressure and volume of a given mass of confined gas are inversely proportional. Oris notes that “the indicator benefits from no inertia, not delaying the accurate and actual depth indication – particularly useful in decompression breaks in lesser depths.”

Features 46mm steel case, water resistant 500 meters. “The special sapphire crystal, 50% thicker than an average top glass, features a channel milled into the side which runs counterclockwise round the dial, stopping between one and two o’clock. At 12 o’clock, a hole leads to this channel. On descent, the air inside the channel is compressed by the surrounding water pressure, allowing water to enter through the hole at 12 o’clock. The edge, in light grey and dark grey, differentiates between water and compressed air on the scale around the outside of the dial, indicating depth while descending or ascending.”

Available at $3,500.