Editing Dive computer (section)

== Special purpose dive computers ==
[[File:JJ Rebreather at Blue Rock Quarry PC290151.jpg|thumb|Dive computer showing three oxygen cell readings from a CCR in the middle row]]
Some dive computers are able to calculate decompression schedules for [[breathing gas]]es other than air, such as [[nitrox]], pure [[oxygen]], [[Trimix (breathing gas)|trimix]] or [[heliox]]. The more basic nitrox dive computers only support one or two gas mixes for each dive. Others support many different mixes.<ref name="Huggins 2006" /> When multiple gases are supported, there may be an option to set those which will be carried on the dive as active, which sets the computer to calculate the decompression schedule and time to surface based on the assumption that the active gases will be used when they are optimal for decompression. Calculation of tissue gas loads will generally follow the gas actually selected by the diver,<ref name="Perdix manual" /> unless there is multiple cylinder pressure monitoring to enable automatic gas selection by the computer.<ref name="iX3M AI" />

Most dive computers calculate decompression for open circuit [[Scuba set|scuba]] where the proportions of the breathing gases are constant for each mix: these are "constant fraction" dive computers. Other dive computers are designed to model the gases in closed circuit scuba ([[diving rebreather]]s), which maintain constant [[partial pressure]]s of gases by varying the proportions of gases in the mixture: these are "constant partial pressure" dive computers. These may be switched over to constant fraction mode if the diver bails out to open circuit.<ref name="Perdix manual" /> There are also dive computers which monitor oxygen partial pressure in real time in combination with a user nominated diluent mixture to provide a real-time updated mix analysis which is then used in the decompression algorithm to provide decompression information.<ref name="HSE Manual" /><ref name="Predator manual" />

===Freediving computers===
<!--target for redirect [[Freediving computer]] -->
A freediving computer, or general purpose dive computer in freediving mode, will record breath hold dive details automatically while the diver is underwater, and the length of the surface interval between dives. It records each dive, so there is a record of the number of dives. This is useful to ensure adequate surface interval to clear carbon dioxide buildup.<ref name="Essex" />

Surface interval times are also useful to monitor to avoid [[taravana]], the freediving decompression sickness. A dive computer is also the most effective way to notify the diver of the depth at which free-fall should start by a free-fall alarm. monitoring descent and ascent speed, and verifying maximum depth are also useful when training for efficiency.<ref name="Zvaritch 2019" /> 

Two types of freediving computer are available, the ones that are dedicated to freediving, and those that are also scuba decompression computers, with a freediving mode. A stopwatch is useful for timing static apnea, rechargeable batteries are an option in some models, and GPS can be useful for spearfishers who wish to mark a place and return to it later. A few models offer a heart rate monitor.<ref name="Zvaritch 2020" />