Editing Dive computer (section)

=== Algorithms ===
<!-- [[Image:MaresM1simul.jpg|thumb|Mares M1 diving computer, showing simulated data]] -->
{{see also|Decompression theory}} 
The decompression algorithms used in dive computers vary between manufacturers and computer models. Examples of [[decompression algorithms]] are the [[Bühlmann algorithm]]s and their variants, the [[Thalmann algorithm|Thalmann VVAL18 Exponential/Linear model]], the [[Varying Permeability Model]], and the [[Reduced Gradient Bubble Model]].<ref name="Azzopardi and Sayer 2010" /> The proprietary names for the algorithms do not always clearly describe the actual decompression model. The algorithm may be a variation of one of the standard algorithms, for example, several versions of the  [[Bühlmann decompression algorithm]] are in use. The algorithm used may be an important consideration in the choice of a dive computer. Dive computers using the same internal electronics and algorithms may be marketed under a variety of brand names.<ref name="Ozygit and Egi 2012" />

The algorithm used is intended to inform the diver of a decompression profile that will keep the risk of [[decompression sickness]] (DCS) to an acceptable level. Researchers use experimental diving programmes or data that has been recorded from previous dives to validate an algorithm. The dive computer measures depth and time, then uses the algorithm to determine decompression requirements or estimate remaining no-stop times at the current depth. An algorithm takes into account the magnitude of pressure reduction, breathing gas changes, repetitive exposures, rate of ascent, and time at altitude. Algorithms are not able to reliably account for age, previous injury, ambient temperature, body type, alcohol consumption, dehydration, and other factors such as [[patent foramen ovale]], because the effects of these factors have not been experimentally quantified, though some may attempt to compensate for these by factoring in user input, and for diver peripheral temperature and workload by having sensors that monitor ambient temperature and cylinder pressure changes as a proxy.<ref name="DipnDive 2021" /> Water temperature is known to be a poor proxy for body temperature, as it does not account for the effectiveness of the diving suit or heat generated by work or active heating systems.<ref name="Pollock 2015a" />

====Choice of algorithm====

There is no conclusive evidence that any currently used algorithm  is significantly better than the others, and by selective setting of the constants, most of them can be made to produce very similar ascent and decompression profiles for a given ingassing profile. When used in the recreational diving range of no-stop exposures on factory settings, it is likely that they are all acceptably safe, though some will clearly be more conservative than others. The question of whether the diver gains anything of value from the higher conservatism is an open question, when the rate of symptomatic decompression sicknesss is very low and the external risk factors are not yet amenable to computational analysis.<ref name="Fogarty 2025" /> Some manufacturers use their unverified and  undisclosed modified algorithms as selling points, usually without making any specific claims about their effectiveness, and the user is in no position to make an educated choice due to the vagueness of the claims.<ref name="DiveGearExpress 2021" /> Some others use algorithms well-defined in the literature, allowing the user who has sufficient understanding of the specific decompression model to make an informed decision. Some of these also allow user modification of settings which modify algorithm conservatism following well defined methods such as gradient factors, further facilitating educated choice.<!--for example Shearwater -->

=====Use of algorithms by manufacturer and model=====

{{as of|2009}}, the newest dive computers on the market used:
* [[Liquivision]] X1: V-Planner Live: VPM-B [[Varying Permeability Model]] and GAP for X1: [[Bühlmann decompression algorithm|Bühlmann]] GF (Buhlman with Gradient Factors){{Citation needed|date=September 2012}}
* [[Mares (scuba gear company)|Mares]]: Mares-Wienke [[Reduced Gradient Bubble Model]]{{Citation needed|date=September 2012}}{{clarify|Is this one of the "folded RGBM" models like the Suunto-Wienke model?|date=June 2021}}
* [[Pelagic Pressure Systems]]: modified [[John Scott Haldane|Haldanean]]/[[Diving Science and Technology|DSAT]] Database or [[Bühlmann decompression algorithm|Bühlmann]] ZH-L16C(called Z+){{Citation needed|date=September 2012}}
* [[Seiko]]: [[Bühlmann decompression algorithm|Bühlmann]] ZH-L12 as modified by Randy Bohrer.<ref name="DH33" />
* [[Suunto]]: Suunto-Wienke [[Reduced Gradient Bubble Model]]. The Suunto folded RGBM is not a true RGBM algorithm, which would be computationally intensive, but a Haldanean model with additional bubble limitation factors.<ref name="Azzopardi and Sayer 2010" />
* [[Uwatec]]: [[Bühlmann decompression algorithm|Bühlmann]] ZH-L8 /ADT (Adaptive), MB (Micro Bubble), PMG (Predictive Multigas), [[Bühlmann decompression algorithm|Bühlmann]] ZH-L16 DD (Trimix){{Citation needed|date=September 2012}}
* Heinrichs Weikamp OSTC and DR5: [[Bühlmann decompression algorithm|Bühlmann]] ZH-L16 and Bühlmann ZH-L16 plus Erik Baker's [[gradient factor]]s deep stop algorithm both for open circuit and fixed set point closed circuit rebreather.{{Citation needed|date=September 2012}}

{{as of|2012}}:

* Cochran EMC-20H: 20-tissue Haldanean model.<ref name="Validation workshop" />
* Cochran VVAL-18: nine-tissue Haldanean model with exponential ongasing and linear offgassing.<ref name="Validation workshop" />
* Delta P: 16-tissue Haldanean model with VGM (variable gradient model, i.e., the tolerated supersaturation levels change during the dive as a function of the profile, but no details are provided as to how this is done).<ref name="Validation workshop" />
* Mares: ten-tissue Haldanean model with RGBM;<ref name="Validation workshop" /> the RGBM part of the model adjusts gradient limits in multiple-dive scenarios through undisclosed "reduction factors".<ref name="RGBM with Basis and Comparison" />{{rp|16–20}}
* Suunto: nine-tissue Haldanean model with RGBM;<ref name="Validation workshop" /> the RGBM part of the model adjusts gradient limits in multiple-dive scenarios through undisclosed "reduction factors".<ref name="RGBM with Basis and Comparison" />{{rp|16–20}}
* Uwatec: ZH-L8 ADT (Adaptive), MB (Micro Bubble), PMG (Predictive Multigas), ZH-L16 DD (Trimix).

{{as of|2019}}:

* Aqualung: Pelagic Z+ – a proprietary algorithm based on Bühlmann ZH-L16C algorithm.<ref name="DipnDive" />
* Cressi: Haldane and Wienke RGBM algorithm.<ref name="DipnDive" />{{clarify|Is this another pseudo RGBM modification?|date=June 2021}}
* Garmin: Bühlmann ZH-L16C algorithm.<ref name="DipnDive" />
* Oceanic: Dual Algorithm: Pelagic Z+ (ZH-L16C) and Pelagic DSAT.<ref name="DipnDive" />
* ScubaPro: ZH-L8 ADT (Adaptive), MB (Micro Bubble), PMG (Predictive Multigas), ZH-L16 DD (Trimix).
* Shearwater: Bühlmann ZH-L16C with user selectable gradient factors or optional VPM-B and VPM-B/GFS.<ref name="DipnDive" /><ref name="Perdix manual" />

{{as of|2021}}:

* Aqualung: Pelagic Z+ – a proprietary algorithm developed by Dr. John E. Lewis, based on Bühlmann ZH-L16C algorithm. Conservatism may be adjusted by altitude setting, deep stops, and safety stops.<ref name="DipnDive 2021" /> 
* Atomic: "Recreational RGBM" based on the Wienke model, using user input of age, selected risk level, and exertion level to adjust conservatism.<ref name="DipnDive 2021" /> 
* Cressi: RGBM. User settings for conservatism and optional deep and safety stops.<ref name="DipnDive 2021" /> 
* Garmin: Bühlmann ZH-L16C, with a choice of three preset conservatism settings or customisable gradient factors, and customisable safety stops.<ref name="DipnDive 2021" />
* Mares: RGBM or Bühlmann ZH-L16C GF (Gradient Factor) depending on model. Preset and customisable conservatism settings.<ref name="DipnDive 2021" />
* Oceanic: User option of dual algorithms: Pelagic Z+ (ZH-L16C) and Pelagic DSAT.<ref name="DipnDive 2021" />
* Oceans: Bühlmann ZH-L16C GF (Gradient Factor). Preset conservatism settings. 
* Ratio: Bühlmann ZH-L16B and VPM-B, user settable Gradient Factors (GFL/GFH) for Bühlmann and user settable Bubble Radius for VPM.
* ScubaPro: ZH-L16 ADT MB PMG. Predictive multi-gas modified algorithm, with various conservatism options with user inputs of experience level, age and physical condition, which are assumed to have some influence on gas elimination rate. Input from breathing rate, skin temperature and heart rate monitor is also available and can be used by the algorithm to estimate a workload condition, which is used to modify the algorithm.<ref name="DipnDive 2021" />
* Shearwater: Bühlmann ZH-L16C with optional VPM-B, VPM-B/GFS and DCIEM. The standard package is Bühlmann with user selectable gradient factors, and the option to enable VPM software which may be used in open-circuit tech and rebreather modes, or enable DCIEM which may be used in air and single-gas nitrox modes. VPM-B/GFS is a combination of the two models which applies the ceiling from the more conservative model for each stop.<ref name="DipnDive 2021" /><ref name="Scubadoc" /> The current decompression ceiling may be displayed as an option and the algorithm will calculate decompression at any depth below the ceiling. The GFS option is a hybrid that automatically chooses the decompression ceiling from the more conservative of the VPM-B profile and a Bühlmann ZH-L16C profile. For the Bühlmann profile a single gradient factor is used, adjustable over a range of 70% (most conservative) to 99% (least conservative), the default is 90%.  The DCIEM model differs from ZH-L16C and VPM which are parallel models and assume that all compartments are exposed to ambient partial pressures and no gas interchange occurs between compartments. A serial model assumes that the diffusion takes place through a series of compartments, and only one is exposed to the ambient partial pressures.<ref name="DiveGearExpress 2021" />
* Suunto: RGBM based algorithm with conservatism settings, known to be a comparatively conservative algorithm. There are various versions used in different models. The technical computers use an algorithm that claims flexibility through the use of continuous decompression, which means the current ceiling is displayed instead of a stop depth.
** RGBM
** Technical RGBM
** Fused RGBM: for deep diving, switches between "RGBM" and "Technical RGBM" for open circuit and rebreather dives to a maximum of 150&nbsp;m<ref name="DipnDive 2021" />
** Fused RGBM 2<ref>{{Cite web |url=https://www.suunto.com/Support/Suunto-rgbm-dive-algorithms/ |title=Suunto RGBM Dive Algorithms |access-date=2021-09-14 |archive-date=2021-09-14 |archive-url=https://web.archive.org/web/20210914034535/https://www.suunto.com/Support/Suunto-rgbm-dive-algorithms/ |url-status=live }}</ref>
** Bühlmann 16 GF (Gradient Factor) based on ZH-L16C<ref>{{Cite web |url=https://www.suunto.com/Support/Product-support/suunto_eon_steel_black/suunto_eon_steel_black/features/decompression-algorithms/ |title=Suunto EON Steel Black User Guide 2.5: Decompression algorithms |access-date=2021-09-18 |archive-date=2021-09-18 |archive-url=https://web.archive.org/web/20210918210657/https://www.suunto.com/Support/Product-support/suunto_eon_steel_black/suunto_eon_steel_black/features/decompression-algorithms/ |url-status=live }}</ref>

{{as of|2023}}:

:[[Shearwater Research]] has supplied dive computers to the US Navy with an exponential/linear algorithm based on the Thalmann algorithm since [[Cochran Undersea Technology]] closed down after the death of the owner. This algorithm is not as of 2024 available to the general public on Shearwater computers, although the algorithm is freely available and known to be lower risk than the Buhlmann algorithm for mixed gas and constant set-point CCR diving at deeper depths, which is the primary market for Shearwater products.<ref name="Doolette 2023" /><ref name="Blömeke 2024" />