A depth gauge is a pressure gauge that displays the equivalent depth in water. It is a piece of diving equipment often used by SCUBA divers. Most modern diving depth gauges' have an electronic mechanism and digital display. Older types used a mechanical mechanism and analogue display. A diver uses a depth gauge with decompression tables and a watch to avoid decompression sickness. A common alternative to the depth gauge, watch and decompression tables is a dive computer. A depth gauge and an oxygen analyser/oxygen sensor can be used to measure the partial pressure of oxygen of the breathing gas, which is necessary to avoid oxygen toxicity. Digital depth gauges commonly also show the interval of time that the diver has been submerged and show the diver's rate of ascent and descent, which can be is useful for avoiding barotrauma. As the gauge only measures pressure, there is an inherent inaccuracy in the depth displayed by most gauges that are used in both fresh water and seawater due to the difference in the densities of fresh water and seawater.
