Water enters the hole under pressure, creating a watermark that corresponds to a depth gauge. A diver's digital wristwatch with a depth gauge function is submerged in the box. One key sharpening parameter is the depth gauge setting. Oris patented the Oris Aquis Depth Gauge, its first mechanical depth gauge, in 2013. The first depth gauge was invented in the late 1800s. Reading the depth gauge gives the apparent depth change between the higher and lower station. A ratio chromatic depth gauge has been found in larvae of the polychaete "Platynereis dumerilii". The main depth gauge must have been knocked out by the depth charges. The depth gauge is the small steel protuberance in front of each cutting tooth. A depth gauge is a pressure gauge that displays the equivalent depth in water. The damaged depth gauge stuck at , so the submarine broached and was again detected. By the early nineteenth century, "the depth gauge was a standard feature on diving bells". The "Boyle-Mariottesche depth gauge" consists of a circular curved glass tube open at one end.