Editing Dive computer (section)

== Validation ==
''Verification'' is the determination that a dive computer functions correctly, in that it correctly executes its programmed algorithm, and this would be a standard quality assurance procedure by the manufacturer, while ''validation'' confirms that the algorithm provides the accepted level of risk.<ref name="Validation" /> The risk of the decompression algorithms programmed into dive computers may be assessed in several ways, including tests on human subjects, monitored pilot programs, comparison to dive profiles with known decompression sickness risk, and comparison to risk models.<ref name="Validation workshop" />

===Performance of dive computers exposed to profiles with known human subject results.===
Studies (2004) at the [[University of Southern California]]'s Catalina hyperbaric chamber ran dive computers against a group of dive profiles that have been tested with human subjects, or have a large number of operational dives on record.<ref name="Huggins, 2004" />

The dive computers were immersed in water inside the chamber and the profiles were run. Remaining no-decompression times, or required total decompression times, were recorded from each computer 1 min prior to departure from each depth in the profile. The results for a 40 msw "low risk" multi-level no-decompression dive from the PADI/DSAT RDP test series<ref name="Hamilton et al., 1994" /> provided a range of 26 min of no-decompression time remaining to 15 min of required decompression time for the computers tested. The computers which indicated required decompression may be regarded as conservative: following the decompression profile of a conservative algorithm or setting will expose the diver to a reduced risk of decompression, but the magnitude of the reduction is unknown. Conversely the more aggressive indications of the computers showing a considerable amount of remaining no-decompression time will expose the diver to a greater risk than the fairly conservative PADI/DSAT schedule, of unknown magnitude.<ref name="Huggins, 2004" />

=== Comparative assessment and validation ===
Evaluation of decompression algorithms could be done without the need for tests on human subjects by establishing a set of previously tested dive profiles with a known risk of decompression sickness. This could provide a rudimentary baseline for dive computer comparisons.<ref name="Validation workshop" /> As of 2012, the accuracy of temperature and depth measurements from computers may lack consistency between models making this type of research difficult.<ref name=Azzopardi2012 />

==== Accuracy of displayed data ====
European standard "EN13319:2000 Diving accessories - Depth gauges and combined depth and time measuring devices - Functional and safety requirements, test methods", specifies functional and safety requirements and accuracy standards for depth and time measurement in dive computers and other instruments measuring water depth by ambient pressure. It does not apply to any other data which may be displayed or used by the instrument.<ref name="Azzopardi and Sayer 2012" /><ref name="EN13319" />

Temperature data are used to correct pressure sensor output, which is non-linear with temperature, and are not as important as pressure for the decompression algorithm, so a lesser level of accuracy is required. A study published in 2021 examined the response time, accuracy and precision of water temperature measurement computers and found that 9 of 12 models were accurate within 0.5&nbsp;°C given sufficient time for the temperature to stabilise, using downloaded data from open water and wet chamber dives in fresh- and seawater. High ambient air temperature is known to affect temperature profiles for several minutes into a dive, depending on the location of the pressure sensor, as the heat transfer from computer body to the water is slowed by factors such as poor thermal conductivity of a plastic housing, internal heat generation, and mounting the sensor orifice in contact with the insulation of the diving suit. An edge-mounted sensor in a small metal housing will follow ambient temperature changes much faster than a base mounted sensor in a large, thick-walled plastic housing, while both provide accurate pressure signals.<ref name="Marlowe et al 2021" />

An earlier survey of 49 models of decompression computer published in 2012 showed a wide range of error in displayed depth and temperature. Temperature measurement is primarily used to ensure correct processing of the depth transducer signal, so measuring the temperature of the pressure transducer is appropriate, and the slow response to external ambient temperature is not relevant to this function, provided that the pressure signal is correctly processed.<ref name=Azzopardi2012 />

Nearly all of the tested computers recorded depths greater than the actual pressure would indicate, and were markedly inaccurate (up to 5%) for some of the computers. There was considerable variability in permitted no-stop bottom times, but for square profile exposures, the computer-generated values tended to be more conservative than tables at depths shallower than 30&nbsp;m, but less conservative at 30–50&nbsp;m. The no-stop limits generated by the computers were compared to the no-stop limits of the DCIEM and RNPL tables.<ref name=Azzopardi2012 /> Variation from applied depth pressure measured in a decompression chamber, where accuracy of pressure measurement instrumentation is periodically calibrated to fairly high precision (±0.25%), showed errors from -0.5 to +2m, with a tendency to increase with depth.<ref name=Azzopardi2012 />

There appeared to be a tendency for models of computer by the same manufacturer to display a similar variance in displayed pressure, which the researchers interpreted as suggesting that the offset could be a deliberate design criterion, but could also be an artifact of using similar components and software by the manufacturer. The importance of these errors for decompression purposes is unknown, as ambient pressure, which is measured directly, but not displayed, is used for decompression calculations. Depth is calculated as a function of pressure, and does not take into account density variations in the water column. Actual linear distance below the surface is more relevant for scientific measurement, while displayed depth is more relevant to forensic examinations of dive computers, and for divers using the computer in gauge mode with standard decompression tables, which are usually set up for pressure in [[Metre sea water|feet or metres of water column]] .<ref name=Azzopardi2012 />