See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/272220875Estimation of depth and temperature in 47 models of divingdecompression computerArticle  in  Underwater Technology The International Journal of the Society for Underwater · November 2012DOI: 10.3723/ut.31.003CITATIONS READS7 1602 authors, including: Martin Dj Sayer University of the Highlands and Islands 104 PUBLICATIONS   1,486 CITATIONS    SEE PROFILESome of the authors of this publication are also working on these related projects: Investigating the environmental benefits of artificial reefs View project All content following this page was uploaded by Martin Dj Sayer on 30 March 2015. The user has requested enhancement of the downloaded file.doi:10.3723/ut.31.003  International Journal of the Society for Underwater Technology, Vol 31, No 1, pp 3–12, 2012 Technical PaperEstimation of depth and temperature in 47 modelsof diving decompression computerElaine Azzopardi* and Martin SayerUK National Facility for Scientific Diving, Scottish Association for Marine Science, Dunbeg,Oban, Argyll, Scotland, PA37 1QA, UKAbstract have discussed how the conversion of pressure to aForty seven models of diving computer were subjected to a depth estimate can be affected by environmentalrange of nominal depths (10, 20, 30, 40 and 50m), in fresh- factors such as altitude (Buzzacott and Ruehle, 2009;water and seawater, in a simulated temperate environment. Sayer, 2010). However, other effects, such as theThe depths downloaded from the computers were adjusted water standards that are used for computer calibra-for density and compared to the published limits of the EU tion and the actual ambient temperature and salin-standard EN13319:2000 for depth-time measurement. The ity, can also have an influence on the conversion.estimated depths for most of the computer models were Irrespective of what methods and assumptionsclose to or within the limits for the standard, but were not have been employed to compute the pressure toalways near to the accuracies claimed by the manufactur- depth conversion, the computers will generate aers. Testing was complicated by the manufacturers’ lack of downloadable dive profile based on depth againstspecification of the salinity standards used by most dive time. For dive computer models that possess acomputers for the conversion of pressure measured to depthdisplayed. The mean estimated depths tended toward the download capability, the dive profile can be a prod-simulated nominal test depths; maxima/minima depth differ- uct of varying volumes of stored information dis-ences from nominal were 2.4m/-1.5m and 1.6m/-0.8m for played at differing rates, increments and resolutionfreshwater and seawater tests, respectively. The results from of measurement or estimation (Azzopardi andthe temperature trials generated a measured range of 5.1°C Sayer, 2010).from nominal values, although the differences in the meth- Dive computers have been applied to studies asods employed either by the computers or the download diverse as marine biology (Collins and Baldock,software to record or display temperature negated stand- 2007); reef measurement (Sayer and Brown, 2010);ardised comparison. It was concluded that caution should pathology (Rutty, 2007); decompression model-be employed when using displayed and/or recorded depth ling (Sayer et al., 2005), in combination with geo-and temperature data from dive computers in scientific or referencing techniques (Kuch et al., 2012; Vacchiforensic studies. et al., 2012); and dive accident investigation (Sayer et al., 2008; Denoble et al., 2009). All such studiesKeywords: dive computers, depth, temperature, seawater,freshwater, EN13319:2000 rely on a relatively accurate conversion from meas- ured pressure to displayed depth. Although the European standard EN13319:2000 addresses depth1. Introduction and time measurement in dive gauges (Sieber et al.,Diving computers are primarily used as tools to mon- 2012), it largely overlooks the fact that total accu-itor and calculate decompression schedules and racy with regard to depth displayed (and recorded)have the advantage over conventional tables because can only be achieved through converting pressurethey compute decompressions for multi-level dives readings in a combination with measured physicaland in real time (e.g. Angelini, 2012; Huggins, 2012). parameters (predominantly water density and tem-In a basic form, a dive computer recalculates the perature). Only Cochran computers are capable ofcumulative decompression loading based on, in adjusting for salinity changes automatically, as theymost cases, the near continuous measurement and have the capability of measuring the conductivity ofrecording of pressure and time. the medium in which they are immersed (Angelini, The depth displayed on a computer is an inter- 2012). All the computers in this study do not havepretation of the pressure measured (Buzzacott and this capability, so they possess in-built assumed cali-Ruehle, 2009; Sieber et al., 2012). Previous studies brations for water density with some ability for the user to switch between set points (usually ‘freshwa- * Contact author. E-mail address: elaine.azzopardi@sams.ac.uk ter’ or ‘seawater’). 3 Azzopardi and Sayer. Estimation of depth and temperature in 47 models of diving decompression computer Nearly all technical manuals that accompany dive tests all other adjustable functions were left on computers upon purchase do not explain the con- default settings. In addition, Gemini Tiny Talk tem- version assumptions being made during the trans- perature loggers were immersed with the comput- formation of pressure measured to depth displayed ers to record water temperature. (Azzopardi and Sayer, 2010). The present study Following each depth test, the stored dive pro- investigates how dive computers display depth when file of each computer was downloaded for analysis. exposed to a number of nominal pressures and set The recompression chamber used in this study was to seawater and freshwater (where this function was calibrated regularly (every six months or less) to a available) at typical operational water densities seawater standard equivalent to 1.02691 kg l-1 and (full seawater against freshwater). Many models within an accepted error of 0.25% of depth. In order also display water temperature, and since this may to compare the performance of the computers be employed in scientific or forensic investigations, against the simulated depth profiles, the depth temperature recording is investigated in temperate (20cm) at which the computers were immersed in water. the water tank was deleted from the download information. Both the resulting freshwater and ­seawater depths were then corrected against the 2. Methods chamber gauge depth using the calibration seawa- At the time of this investigation there were 47 models ter standard density. The height of air above the of dive computer in common use in the UK made water surface of the test tank and the take-off for by 14 different manufacturers. An example of each the chamber gauge measurement did not signifi- of the models was purchased from independent cantly affect any adjustment for depth and so was retail sources. Although all computers were sub- not considered. jected to the following tests, limitations in displays or downloaded information meant that sample num- 2.2. Temperature bers varied between tests. Details of all the comput- The temperature tests were carried out over a sim- ers used in this study are given in Tables 1 and 2. ulated temperate temperature regime (nominally Statistical analyses were by Student’s t   -tests follow- 12–17°C). The data were obtained during the depth ing Lilliefors adapted Kolmogorov–Smirnov tests tests described earlier with the computers immersed for normality. All data were stored and analysed to 20cm depth. Total immersion time usually using Microsoft Excel. A record of any computer exceeded 60min. The built-in dive chamber envi- malfunctions or failures was maintained. ronmental control unit was set to maintain an air temperature of 26 ± 1°C during the temperature 2.1. Depth fluctuations caused by the actions of compression Depth measurement tests were conducted to a and decompression. Two or three calibrated temper- ­simulated nominal maximum depth equivalent of ature loggers were put into each container of com- 50msw (metres of seawater) in 10msw increments. puters to provide a reference water temperature. Henceforth in this paper, the simulated nominal As before, the computers were downloaded after depths for both seawater and freshwater trials are each test and the readings given in the download given only as metres depth irrespective of whether profiles or data logs were used in the final analysis. they have been adjusted for respective media densi- However, for temperature, the downloaded data ties (discussed later). were not recorded or displayed in a uniform man- In each test, the computers were immersed to ner between different brands of computer or even 20cm in a tank of either seawater (SW: 33‰S) or between different models of the same brand. For freshwater (FW: 1‰S) located inside a standard example, not all downloads gave the maximum and two-compartment therapeutic recompression cham- minimum temperatures recorded during a dive. A ber (Divex2000). The chamber was compressed on number of brands, such as Mares, Oceanic, Citizen, air to a simulated nominal depth equivalent 50m, Beuchat, Seeman Sub, Scubapro and the Aladin and then the pressure was released to the depths of Pro Ultra, only gave the minimum temperature 40m, 30m, 20m and 10m before surfacing. The recorded during a dive. Suunto downloads gave the computers were left at each depth for a minimum temperatures at the start and end of the dive, as of 5min to allow for models with slower recording well as at the maximum depth, although occasion- intervals to register the depths displayed. Five to ally supplemental information could be obtained eight replicate trials of each test were carried out in from the temperature readings in the profile list. both freshwater and seawater, with the computers Cressi Sub, Tusa and Apeks computers only gave set to the correct environment mode (FW or SW), the water temperature at the maximum depth. Most where this function was available. Throughout the of the Uwatec models, with the exception of Pro4 Vol 31, No 1, 2012Table 1: Mean and range of depth (m) downloaded from 47 models of diving computer immersed in freshwater over a range ofnominal depths (10–50m, n = 5–7 in each case). Computers with the facility to switch to a freshwater mode are indicated by ‘Y’;those without are indicated by ‘N’; blanks indicate those where a switch mechanism was not evident (Azzopardi and Sayer,2010). An asterisk indicates where a computer was tested but no useable data could be recovered from the downloadManufacturer Model 50m 40m 30m 20m 10m(Brand)APEKS Quantum Y 52.1 (52.0–52.4) 41.9 (41.8–42.1) 31.4 (31.4–31.6) 21.0 (21.0–21.0) 10.4 (10.4–10.6) Pulse Y 51.0 (50.8–51.1) 41.0 (40.9–41.2) 30.6 (30.5–30.7) 20.3 (20.2–20.4) 10.1 (10.0–10.2)BEAUCHAT Voyager N 49.3 (48.8–49.3) 39.5 (39.5–39.5) 28.8 (28.7–29.2) 19.1 (18.9–19.4)   9.4 (9.1–9.6)BUDDY Nexus* Y – – – – –CITIZEN Cyber Aqualand N 49.2 (49.0–49.4) 39.5 (39.3–39.6) 29.4 (29.3–29.5) 19.6 (19.5–19.6)   9.7 (9.6–9.8)CRESSI SUB Archimede 2 N 49.5 (49.4–49.5) 39.8 (39.6–40.0) 29.6 (29.5–29.8) 19.7 (19.6–20.0)   9.8 (9.7–9.9) Edy II N 49.4 (49.3–49.5) 39.7 (39.6–39.9) 29.6 (29.5–29.7) 19.7 (19.6–19.8)   9.8 (9.8–9.9)DELTA P VRX N 49.4 (49.2–49.6) 39.7 (39.5–39.8) 29.6 (29.5–29.7) 19.7 (19.7–19.8)   9.8 (9.7–10.0) VR 3-1 N 49.4 (49.2–49.6) 39.7 (39.5–39.8) 29.7 (29.6–29.7) 19.7 (19.7–19.8)   9.8 (9.6–9.9) VR 3-2 N 49.4 (49.2–49.5) 39.6 (39.4–39.8) 29.6 (29.4–29.7) 19.7 (19.6–19.8)   9.8 (9.6–9.9)MARES Nemo Y 50.4 (50.3–50.6) 40.5 (40.4–40.6) 30.3 (30.2–30.4) 20.2 (20.1–20.3) 10.1 (10.0–10.2) Nemo Sport 49.7 (49.6–49.8) 39.8 (39.6–39.9) 29.7 (29.6–29.8) 19.8 (19.6–20.0)   9.9 (9.7–10.2) Nemo Air Y 50.3 (50.2–50.5) 40.4 (40.2–40.7) 30.1 (30.0–30.3) 20.1 (19.9–20.3) 10.0 (9.8–10.2) Nemo Excel Y 50.5 (50.4–50.7) 40.6 (40.5–40.7) 30.3 (30.2–30.4) 20.2 (20.1–20.4) 10.1 (10.0–10.3) Nemo Wide Y 50.3 (50.2–50.5) 40.4 (40.3–40.6) 30.2 (30.1–30.3) 20.1 (20.0–20.2) 10.0 (9.9–10.0) Puck wrist Y 50.4 (50.2–50.6) 40.5 (40.3–40.6) 30.2 (30.1–30.3) 20.2 (20.1–20.3) 10.1 (9.9–10.2) Puck Air Y 50.3 (50.2–50.6) 40.5 (40.3–40.8) 30.2 (30.1–30.3) 20.1 (20.0–20.3) 10.0 (9.9–10.2)OCEANIC Veo 250 N 49.2 (48.5–50.3) 39.4 (38.9–40.8) 29.5 (29.1–30.3) 19.6 (19.2–20.1)   9.7 (9.4–10.3) VT 3 N 49.2 (49.4–49.8) 39.5 (39.3–39.7) 29.6 (29.5–29.7) 19.7 (19.6–19.9)   9.8 (9.7–9.9) Pro Plus 2 49.0 (48.8–49.4) 39.3 (38.9–39.5) 29.4 (29.1–29.7) 19.5 (19.2–19.8)   9.8 (9.7–10.0) Atom 2 49.2 (48.9–49.4) 39.6 (39.5–39.7) 29.7 (29.6–29.8) 19.8 (19.7–19.9)   9.9 (9.8–10.1) Datamask Hud N 49.3 (49.0–49.4) 39.6 (39.5–39.7) 29.5 (29.5–29.6) 19.7 (19.6–19.8)   9.8 (9.7–9.9)SCUBAPRO Xtender N 49.5 (49.4–49.6) 39.9 (39.8–40.1) 29.9 (29.7–30.0) 19.9 (19.8–20.0)   9.8 (9.7–9.9)SEEMAN XP 5 N 49.0 (48.8–49.1) 39.2 (39.2–39.2) 29.2 (29.1–29.4) 19.5 (19.5–19.6)   9.7 (9.7–10.0)SUUNTO D9 N 49.5 (49.2–49.6) 39.7 (39.6–39.8) 29.7 (29.6–29.7) 19.8 (19.7–19.8)   9.8 (9.8–9.9) D6 N 49.5 (49.3–49.6) 39.7 (39.6–39.8) 29.7 (29.6–29.8) 19.8 (19.7–19.9)   9.9 (9.8–10.0) D4 N 49.5 (49.4–49.6) 39.8 (39.7–39.9) 29.7 (29.6–29.9) 19.8 (19.8–20.0)   9.9 (9.8–10.1) Stinger N 49.4 (49.1–49.7) 39.6 (39.5–39.8) 29.6 (29.4–29.7) 19.7 (19.5–19.8)   9.8 (9.7–10.0) Spyder N 49.0 (48.8–49.1) 39.4 (39.2–39.5) 29.4 (29.1–29.4) 19.5 (19.2–19.5)   9.7 (9.4–9.7) Vytec DS black N 49.6 (49.4–49.7) 40.0 (39.8–40.1) 29.9 (29.7–30.0) 19.8 (19.8–20.1) 10.0 (10.0–10.0) Vytec silver N 49.6 (49.4–49.7) 39.8 (39.5–39.8) 29.8 (29.7–30.0) 19.9 (19.8–20.1) 10.0 (10.0–10.0) Cobra 2 N 49.6 (49.4–49.8) 39.8 (39.7–39.9) 29.8 (29.7–29.9) 19.9 (19.8–20.0)   9.9 (9.8–10.0) Cobra 3 N 49.8 (49.6–50.0) 40.0 (39.9–40.1) 29.9 (29.8–30.0) 19.9 (19.8–20.0)   9.9 (9.8–10.0) Vyper N 49.7 (49.4–50.0) 39.9 (39.8–40.1) 30.0 (29.7–30.0) 20.0 (19.8–20.1) 10.0 (10.0–10.3) Vyper 2 N 49.5 (49.3–49.6) 39.8 (39.7–39.8) 29.7 (29.6–29.8) 19.8 (19.7–19.9)   9.8 (9.8–9.9) Vyper Air N 49.8 (49.6–50.0) 40.0 (39.9–40.1) 29.9 (29.8–29.9) 19.9 (19.8–20.0)   9.9 (9.8–10.0)TUSA DC Sapience Y 50.9 (50.8–51.1) 41.0 (40.9–41.2) 30.7 (30.6–30.8) 20.4 (20.3–20.5) 10.1 (10.0–10.2) DC Hunter Y 51.0 (50.8–51.2) 41.0 (40.9–41.1) 30.7 (30.6–30.8) 20.4 (20.3–20.5) 10.0 (9.9–10.1)UEMIS SDA Y 51.4 (51.3–51.5) 41.2 (41.1–41.3) 30.7 (30.7–30.8) 20.5 (20.5–20.6) 10.2 (10.2–10.2)UWATEC Galileo Sol Y 50.4 (50.2–50.5) 40.5 (40.3–40.6) 30.2 (30.0–30.3) 20.1 (20.0–20.2) 10.0 (9.9–10.1) Galileo Terra Y 50.4 (50.2–50.6) 40.5 (40.4–40.6) 30.2 (30.1–30.3) 20.1 (20.0–20.2) 10.0 (9.9–10.1) Smart Tec N 50.4 (50.3–50.6) 40.5 (40.4–40.6) 30.2 (30.2–30.3) 20.2 (20.1–20.3) 10.0 (10.0–10.1) Smart Com N 50.5 (50.4–50.6) 40.6 (40.4–40.8) 30.3 (30.2–30.4) 20.2 (20.1–20.3) 10.1 (10.0–10.2) Aladin Pro Ultra N 50.4 (50.2–50.5) 40.4 (40.3–40.4) 30.1 (30.0–30.1) 20.0 (19.9–20.0) 10.0 (9.9–10.1) Aladin Tec2G Y 50.4 (50.3–50.6) 40.5 (40.3–40.7) 30.2 (30.2–30.3) 20.2 (20.1–20.2) 10.0 (10.0–10.1) Aladin prime N 49.2 (49.0–49.3) 39.5 (39.4–39.6) 29.5 (29.4–29.7) 19.7 (19.5–19.7)   9.8 (9.7–10.0) Aladin One N 49.2 (49.1–49.3) 39.5 (39.4–39.6) 29.5 (29.4–29.6) 19.7 (19.6–19.8)   9.8 (9.7–10.0) 5 Azzopardi and Sayer. Estimation of depth and temperature in 47 models of diving decompression computer Table 2: Mean and range of depth (m) downloaded from 47 models of diving computer immersed in seawater over a range of nominal depths (10–50m, n = 5–7 in each case). An asterisk indicates where a computer was tested but no useable data could be recovered from the download Manufacturer Model 50m 40m 30m 20m 10m (Brand) APEKS Quantum 51.5 (51.4–51.6) 41.4 (41.3–41.5) 31.0 (30.9–31.2) 20.8 (20.6–20.8) 10.3 (10.3–10.4) Pulse 50.3 (50.2–50.5) 40.4 (40.3–40.5) 30.1 (30.1–30.2) 20.0 (19.9–20.0)   9.9 (9.9–10.0) BEAUCHAT Voyager 50.1 (50.1–50.1) 40.0 (39.6–40.1) 29.3 (29.2–29.7) 19.3 (19.2–19.7)   9.4 (9.3–9.8) BUDDY Nexus* – – – – – CITIZEN Cyber Aqualand 50.1 (50.0–50.3) 40.1 (40.0–40.2) 29.9 (29.9–30.0) 19.9 (19.8–20.0)   9.9 (9.8–10.0) CRESSI SUB Archimede 2 50.5 (50.3–51.2) 40.4 (40.3–40.5) 30.1 (30.0–30.3) 20.0 (19.9–20.1) 10.0 (9.9–10.1) Edy II 50.3 (50.2–50.4) 40.4 (40.3–40.4) 30.0 (30.0–30.1) 20.0 (19.9–20.1) 10.0 (10.0–10.1) DELTA P VRX 50.3 (50.3–50.5) 40.4 (40.3–40.5) 30.2 (30.1–30.3) 20.1 (20.0–20.2) 10.0 (10.0–10.1) VR 3-1 50.3 (50.2–50.4) 40.4 (40.2–40.4) 30.2 (30.1–30.3) 20.0 (20.0–20.1) 10.0 (10.0–10.1) VR 3-2 50.3 (50.2–50.4) 40.3 (40.2–40.4) 30.1 (30.0–30.2) 20.0 (20.0–20.0) 10.0 (9.9–10.2) MARES Nemo 50.0 (49.9–50.2) 40.1 (40.0–40.3) 30.0 (29.9–30.2) 20.0 (19.9–20.2) 10.0 (9.9–10.2) Nemo Sport 50.6 (50.5–50.8) 40.4 (40.2–40.4) 30.2 (30.0–30.3) 20.0 (19.9 –20.1)   9.9 (9.9–10.0) Nemo Air 50.0 (49.9–50.2) 40.1 (40.0–40.3) 29.9 (29.9–30.1) 19.9 (19.9–20.1)   9.9 (9.9–10.1) Nemo Excel 50.0 (49.9–50.2) 40.2 (40.1–40.2) 30.0 (29.9–30.1) 20.0 (19.9 –20.1) 10.0 (10.0–10.1) Nemo Wide 49.9 (49.9–50.0) 40.0 (39.9–40.0) 29.8 (29.8–29.9) 19.9 (19.8–19.9)   9.9 (9.9–9.9) Puck wrist 50.0 (49.8–50.1) 40.1 (39.9–40.2) 29.9 (29.7–30.0) 19.9 (19.7–20.0)   9.9 (9.7–10.0) Puck Air 50.0 (49.9–50.3) 40.1 (40.0–40.2) 29.9 (29.9–30.1) 20.0 (19.9–20.1) 10.0 (9.9–10.1) OCEANIC Veo 250 50.2 (49.9–51.4) 40.3 (40.1–41.4) 30.1 (29.9–30.8) 20.1 (19.8–20.4) 10.1 (9.9–10.2) VT 3 50.2 (50.0–50.3) 40.3 (40.1–40.3) 30.1 (30.1–30.2) 20.1 (20.0–20.2) 10.1 (10.1–10.2) Pro Plus 2 49.6 (49.6–49.9) 39.8 (39.8–39.8) 29.6 (29.6–29.9) 19.8 (19.8–19.8)   9.9 (9.9–9.9) Atom 2 50.1 (50.0–50.2) 40.3 (40.2–40.4) 30.1 (30.1–30.2) 20.1 (20.0–20.2) 10.0 (10.0–10.1) Datamask Hud 50.3 (50.2–50.3) 40.3 (40.3–40.4) 30.2 (30.1–30.2) 20.1 (20.0–20.2) 10.1 (10.1–10.1) SCUBAPRO Xtender 50.4 (50.3–50.6) 40.6 (40.4–40.6) 30.3 (30.3–30.3) 20.2 (20.1–20.2)   9.9 (9.9–10.0) SEEMAN XP 5 49.8 (49.6–49.9) 39.9 (39.8–40.1) 29.7 (29.6–29.9) 19.8 (19.8–19.8)   9.9 (9.9–9.9) SUUNTO D9 50.3 (50.3–50.5) 40.4 (40.3–40.4) 30.1 (30.1–30.2) 20.1 (20.1–20.1) 10.0 (10.0–10.1) D6 50.3 (50.3–50.5) 40.3 (40.3–40.4) 30.1 (30.1–30.3) 20.1 (20.0–20.1) 10.0 (10.0–10.2) D4 50.4 (50.3–50.5) 40.4 (40.3–40.4) 30.2 (30.2–30.3) 20.1 (20.1–20.2) 10.1 (10.1–10.2) Stinger 50.2 (49.9–50.5) 40.2 (40.1–40.4) 30.1 (29.9–30.2) 20.0 (19.8–20.1) 10.0 (9.9–10.2) Spyder 50.0 (49.9–50.2) 40.0 (39.8–40.1) 29.8 (29.3–30.2) 19.8 (19.2–20.1)   9.6 (9.2–9.9) Vytec DS black 50.5 (50.5–50.5) 40.5 (40.4–40.7) 30.3 (30.2–30.5) 20.1 (20.1–20.1) 10.2 (10.2–10.2) Vytec silver 50.4 (50.2–50.5) 40.5 (40.4–40.7) 30.3 (30.2–30.5) 20.2 (20.1–20.4) 10.2 (10.2–10.2) Cobra 2 50.5 (50.5–50.7) 40.5 (40.4–40.5) 30.2 (30.2–30.3) 20.2 (20.1–20.2) 10.1 (10.1–10.2) Cobra 3 50.7 (50.7–50.9) 40.7 (40.6–40.7) 30.3 (30.3–30.4) 20.2 (20.1–20.2) 10.0 (10.0–10.1) Vyper 50.4 (50.2–50.5) 40.5 (40.4–40.7) 30.2 (30.2–30.2) 20.2 (20.1–20.4) 10.2 (10.2–10.2) Vyper 2 50.4 (50.3–50.5) 40.3 (40.3–40.4) 30.2 (30.1–30.3) 20.1 (20.0–20.2) 10.0 (10.0–10.1) Vyper Air 50.7 (50.7–50.9) 40.7 (40.5–40.7) 30.3 (30.3–30.4) 20.2 (20.2–20.3) 10.0 (10.0–10.1) TUSA DC Sapience 50.3 (50.2–50.4) 40.4 (40.3–40.6) 30.3 (30.2–30.3) 20.1 (20.0–20.2)   9.9 (9.9–10.0) DC Hunter 50.5 (50.4–50.5) 40.5 (40.4–40.6) 30.2 (30.2–30.3) 20.1 (20.1–20.2)   9.9 (9.9–10.0) UEMIS SDA 50.4 (50.4–50.5) 40.4 (40.4–40.5) 30.2 (30.1–30.3) 20.1 (20.1–20.2) 10.0 (10.0–10.1) UWATEC Galileo Sol 50.0 (49.9–50.2) 40.1 (40.0–40.1) 29.9 (29.8–30.0) 20.0 (19.9–20.1)   9.9 (9.9–10.0) Galileo Terra 50.2 (50.1–50.3) 40.2 (40.1–40.2) 30.0 (29.9–30.1) 20.0 (19.9–20.1) 10.0 (9.9–10.1) Smart Tec 51.3 (51.2–51.4) 41.1 (41.0–41.2) 30.7 (30.6–30.8) 20.4 (20.4–20.5) 10.2 (10.2–10.3) Smart Com 51.3 (51.3–51.5) 41.2 (41.1–41.2) 30.7 (30.7–30.8) 20.5 (20.5–20.6) 10.3 (10.3–10.4) Aladin Pro Ultra 51.2 (51.1–51.3) 41.0 (40.9–41.0) 30.5 (30.5–30.6) 20.3 (20.3–20.5) 10.1 (10.1–10.3) Aladin Tec2G 50.1 (50.1–50.2) 40.1 (40.0–40.1) 30.0 (29.9–30.0) 20.0 (20.0–20.0) 10.0 (10.0–10.0) Aladin prime 50.1 (50.0–50.2) 40.1 (40.1–40.2) 30.0 (30.0–30.0) 20.0 (20.0–20.1) 10.0 (10.0–10.0) Aladin One 50.1 (50.0–50.2) 40.2 (40.1–40.2) 30.0 (30.0–30.1) 20.0 (20.0–20.1) 10.0 (10.0–10.1)6 Vol 31, No 1, 2012Ultra, gave a temperature profile throughout thedive, as did the Delta P and Uemis computers. Notemperature reading was obtained from the BuddyNexus downloads, although this is not to say thatthe temperature was not displayed and recorded bythe computer during dives. In some cases there were differences in the valuesgiven in the downloaded data. For example, in theUwatec software program, SmartTrak, temperaturereadings occasionally differed between the down-loaded log book and the download graphic display Fig 2: Bubble plot of estimated minus nominal depthsof the dive profile; this was also the case with some (m, mean • and range; n = 276 for each test depth) for allmodels in the Oceanic series. In order to standardise test computers immersed in seawater and subjected to athe results as much as possible, the log book read- nominal depth range of 10–50m. Diameter of bubbleings were used. Irrespective of how the data were represents the percentage of results for each nominal depthdisplayed (and recorded), minimum temperaturereadings were taken in each case for the analyses.3. Results3.1. Depth displayDuring all the depth trials, the temperatures of thetest waters (measured by calibrated Gemini Tiny Talktemperature loggers) fluctuated by a mean value of1.6°C (with a range of 0.9–2.1°C). The mean andrange of depth displayed for each computer testedat each nominal depth is given in Tables 1 and 2(freshwater and seawater, respectively). In general, the predominant trend (followingadjustment) for most computers was to give esti- Fig 3: Estimated minus nominal depth (m, μ ± sd;mated depths that were close to nominal values n = 276–320 in each case) for all test computers immersed(Figs 1 and 2). When tested in seawater, the esti- in seawater (shaded bars) and freshwater (open bars) over amated mean computer depths were deeper than nominal depth range of 10–50mnominal in comparison to depths in freshwater, butwith less variance (Fig 3). Taken as a percentage of depth ranged from 4.7% to 5.9% in freshwater andthe nominal depth, the difference for the overall from 3.2% to 4.1% in seawater. Minimum valuesmean estimate values ranged from -0.8% to 0.1% were -2.7% to -8.8% in freshwater and -0.8% toin freshwater and -0.1% to 0.9% in seawater. The -8.4% in seawater.overall maximum depth estimates for each nominal Although there was a trend for the computers to display deeper depth readings in seawater, this was not significant (P > 0.05 in all cases). Computers that could be set to a FW mode tended to give depth estimates that were deeper than those that could not be switched; however, the trend was not significant in any of the nominal test depth groups (P > 0.05 in all cases). Some units gave estimated depth values that were consistently deeper than nominal (e.g. Apeks Quantum); some tended to read low over certain depths (e.g. Beuchat Voyager); but the majority of models produced relatively consistent and accu-Fig 1: Bubble plot of estimated minus nominal depths rate results (mostly within 1% of nominal) across(m, mean • and range; n = 315–320 for each test depth) for the depths tested and between the two water typesall test computers immersed in freshwater and subjected to (see Tables 1 and 2). Although tested in both media,a nominal depth range of 10–50m. Diameter of bubble the Buddy Nexus unit tested did not produce usea-represents the percentage of results for each nominal depth ble depth data on download. 7 Azzopardi and Sayer. Estimation of depth and temperature in 47 models of diving decompression computer The results from the repeated exposures to the same depth in both types of water showed varying ranges of estimated depth from the same model of computer (see Tables 1 and 2). Ignoring how close the estimated depths were to the nominal values, there were a small number of outcomes (n = 5–8 in all cases) from replicate trials where the same com- puter produced identical depth displays for all tests at a single nominal depth (2.6% in freshwater trials; 9.1% in seawater; n = 230 in both cases). No model tested produced perfect, repeated depth estimates for every depth/trial combination, as there was Fig 4: Bubble plot of recorded temperature display against always some variation either within depth or nominal median temperature (°C) for all test computers (total between the depths tested. sample n = 800). Diameter of bubble represents the percent- Overall for the five depths tested, in freshwater age of results for each of the 10 temperature tests trials 41 out of the 46 units that gave depth esti- mates produced maximum ranges of replicate dis- played depths of ≤0.5m, and in the seawater trials, 4. Discussion there were 42 out of 46 units. However, of those The present study has demonstrated that, in gen- only one computer model (the Uemis) produced eral, dive computers can vary in their reliability as maximum ranges that were ≤0.2m in the freshwater tools for measuring water depth or temperature exposures, compared with 22 of the computer accurately. This is not particularly surprising for models in seawater. depth, as the conversion from pressure measured There were four and three computers in the to depth displayed requires the accurate measure- freshwater and seawater trials, respectively, that ment of a number of factors (e.g. water density, produced maximum repeat ranges of between temperature) that are outside the operational 0.6m and 0.9m. Only one computer, the Oceanic capability of a relatively limited dive decompres- Veo 250, was able to produce maximum ranges of sion computer. The accurate measurement of the depths displayed more than 1.0m, and did so depth is not crucial to the predominant function both for freshwater (maximum = 1.9m) and seawa- of a dive computer, which is computing decom- ter (maximum = 1.5m). The only instance of a unit pression obligations (discussed later). However, producing an overall maximum range of 0.1m was European standards (e.g. EN13319:2000) do give the Mare Nemo Wide, in seawater (see Table 2). stated limits for the pressure to depth conversion. Similarly, some of the published technical litera- 3.2. Temperature ture supplied with these computers does state The measured nominal temperature environments ‘accuracy’ levels for depth and temperature representative of temperate regimes had a mean recording. value of 16.7°C, with a range of 10.9–18.9°C (n = With temperature, it is suggested that the display 239). The overall recorded temperature informa- and recording by dive computers is a by-product of tion from all the diving computers is shown in Fig 4. some information being generated through having The data present considerable variation in the accu- temperature-compensated pressure sensors in the racy of temperature measurement: overall variance computers. The computers tested did not always for the measured nominal values was 5.1°C (with a produce reliable recorded (downloaded) tempera- range of -4.0°C to 1.1°C; Figure 4). Some of this ture information. It is therefore suggested that dive distribution is attributable to the difficulty in estab- computers are not a suitable tool for the measure- lishing a uniform method for extracting the tem- ment of temperature. perature data from the downloaded information. Although a total of 47 models of dive computer were employed in this study, it is acknowledged that 3.3. Failures and maintenance rates only single samples of each model were tested. As Including pilot studies, the test computers were sub- such, no explicit assertions can be made in relation jected to 2401 computer dives, totalling 2008 com- to any specific model of computer. It is accepted puter hours. During the tests, 41 battery changes that all recordings relate only to the individual were made at the overall rate of one battery change computer model, and even that similar models every 49hr of diving, or 58.6 dives. One unit failed from the same manufacturer cannot be accepted as in a way that would have impacted a dive. true test replicates.8 Vol 31, No 1, 20124.1. Depth However, this may only be the case for the graphicDive computers do not measure depth directly. representation of a dive profile, as a spreadsheetInstead readings are taken from the pressure sensor function listed the depths with a higher resolutionat set time intervals, which are then converted into (as used in the present study). Finally, some errordepth readings on the computer display (Buzzacott could have been added into the trials through slightand Ruehle, 2009; Sieber et al., 2012). The pressure differences in the test pressures, which were moni-may be measured and recorded at relatively high tored using an analogue depth gauge. However,frequency rates for use in calculating decompres- any errors would have been identical for all thesion schedules and, it is assumed, at high levels of computers tested in each run.accuracy. The depth display on the dive computer Although it was not intended to strictly mimicor in the download on a PC is a product of convert- the test conditions outlined in EN13319:2000, theing the pressure sensor reading to a displayed test pressures, salinities and temperatures in thedepth and is not itself used in any decompression present study could not be controlled to the levelscalculations. For example, Cressi Sub computers outlined in the standard. In addition, there is nomeasure pressure every second, but this is only con- guidance given in EN13319:2000 on how to incor-verted to a depth reading for the download display porate the ability of some dive computers to switchevery 30s (Cressi, pers. comm.). Similarly, the Uemis between seawater and freshwater modes into anySDA samples pressure every 625ms, but converts it depth testing.to a depth download display every 5s (Uemis, pers. The ability to switch modes may be meaninglesscomm.). within the context of the present study, as there is a Much of the disparity between sampling frequency near total lack of information given by manufactur-and download recording/display is determined by ers on the standards used for freshwater or seawa-the data memory, resulting from computational ter. The mix of computers that could or could notand unit size compromises made when designing a switch between modes (Table 1), plus the lack ofdive computer. The differences in the recording published calibration standards for all the test com-frequencies and techniques employed in the con- puters, means that there was a number of groups ofversion from pressure readings to depth download computers that were being tested less than ideallydata may have caused some discrepancies between in the present study.the models examined. Azzopardi and Sayer (2010) There was also the issue of trying to determinedetailed the different methods of displaying depth which dive computers were manufactured to adhereinformation (e.g. maximum depth per recording to EN13319:2000. Sieber et al. (2012) discussed theincrement; the depth at the point of making the range of standards that can be applied to dive com-recording; and the average depth over the record- puters and tried to determine from the respectiveing interval) and the resolution of depth displayed accompanying technical notes which were being(0.1m, 0.3m or 0.5m). employed for each type of dive computer. Five out The method of recording should not have made of fifteen dive computer models or manuals exam-any differences in the present study, because the ined by Sieber et al. (2012) did not refer tocomputers were held at the nominal depths for EN13319:2000. With this in mind, the intention ofdurations much longer than the display rates of all the present study was to assess the performancethe computers. However, the methods used to deter- of the dive computers in realistic conditions for mostmine when or how the depths changed between the types of diving. In general, the models tested weredisplay resolution depths was unclear in all manuals. predominantly within the EN13319:2000 limitsThis should only be a significant issue where the when corrected for salinity (Tables 1 and 2).resolution is 0.3m (AP valves Buddy Nexus) or 0.5m In addition to some operational limits set by the(Apeks Quantum, Tusa DC Sapiance, Tusa DC standard, manufacturers also tended to state theirHunter; see Azzopardi and Sayer, 2010). In these own ranges of accuracy in the supporting technicalcases, it is unclear what the threshold levels are for manuals. A number of manufacturers claimed achanging the depth displayed. depth accuracy of ±1% of the full scale, for exam- One other possible source of error was that the ple all the Oceanic, Seeman Sub and Beuchatvalues given in the downloads were not necessarily computers, and all the Mares computers exceptthe same as those that would have been shown by a the Nemo Sport (Oceanic, 2002a,b, 2005, 2006,computer during a dive. For example, the Delta P 2007, 2009; Beuchat, 2004; Seeman, 2004; Mares,computers displayed depth with a resolution of 2005, 2008a–e). Some, namely Suunto and Cressi-0.1m during a dive, but only gave this to the nearest Sub, stipulated ±1% of the full scale, but only when1m in the download (VR Technology, pers. comm.). at 20°C (Cressi-Sub, n.d. a,b; Suunto, n.d. a,b, 2005, 9 Azzopardi and Sayer. Estimation of depth and temperature in 47 models of diving decompression computer 2006a–e, 2007a–c, 2008a,b). The Uwatec Galileo 4.2. Temperature Sol, Terra and Luna models all claimed to have an The lack of uniformity in temperature recording accuracy of 2% ±0.2m (Scubapro-Uwatec, n.d. a–c), and display methods across the various brands while the Tusa and Apeks computers claimed an complicated any overall comparison of the results. accuracy of ±3% for 0.5m in their depth displays A number of claimed accuracies for temperature (Apeks, 2003a,b; Tusa, 2004a,b). were made by some manufacturers. For example, No assertion was made about the accuracy of the Tusa, Apeks and Mares computers, with the excep- Scubapro Xtender or the Mares Nemo Sport com- tion of the Mares Nemo Sport, all claim an accu- puters, and no accuracy claims were found for racy of ±2°C in temperature recording (Apeks, Delta P’s VR3 and VRX computers or for the Uemis 2003a,b; Tusa, 2004a,b; Mares, 2005, 2008a–e). SDA (Mares, 2007; Scubapro-Uwatec, n.d. d; Uemis, Suunto also claim accuracy of ±2°C but only within 2009; VR Technology, 2009). Although some 20min of the temperature changing, whereas the ­accuracy claims were made over the full depth Cressi Sub accuracy claim of ±2°C was for within a range as a plus/minus percentage of the depth dis- 10min change in temperature (Cressi-Sub, n.d. a,b; played, these were more likely not attained in the Suunto, n.d. a,b, 2005, 2006a–e, 2007a–c, 2008a,b). present study at the shallower test depths (10m Citizen claimed its computer models were accurate and 20m). within a ±3°C envelope (Citizen, n.d). In general, In addition, irrespective of whether the compu- there was little if any standardisation in recording ter had the facility to switch between seawater and or displaying temperature. It can only be assumed freshwater modes, the overall trend was for the that any form of accurate temperature measure- computers to be more variable in freshwater. The ment was not a primary design factor for most div- problems with producing accurate depth estimates ing computers. in seawater is that its salinity (and hence its density) can only be assumed. Whereas EN13319:2000 ­suggests a seawater density of 1.0197 kg l-1, manu- 5. Conclusions facturers can use values such as 1.018 kg l-1 or The lack of replication in the computer models 1.025 kg l-1 as standard densities for the pressure/ used in this study is acknowledged, although it was depth conversion (pers. comm. various computer thought likely that models from the same manufac- engineers). turer would behave similarly during both the depth Temperature also affects density, with water and temperature trials. However, this was not the becoming denser at colder temperatures. It is case for many of the manufacturer groups, and so a assumed that temperature changes are included in standard methodology for converting physical the algorithms estimating depth from pressure, measurements to displayed or recorded informa- because the pressure sensors are temperature-com- tion cannot be assumed to be manufacturer-spe- pensated. However, the fact that dive computers do cific. This may be caused, in part, by different age not measure density means that there will always be groups of computer having different conversion some error in depth ‘measurement’ where the den- methodologies. sity standards do not match the salinity of the Pressure measurement is the only barometric medium being dived in. parameter that is imported into decompression Dive computers have been used for depth meas- algorithms to calculate and manage dive profiles. urement for a range of differing applications (Sayer This means that totally accurate depth information et al., 2005; Collins and Baldock, 2007; Rutty 2007; is not an essential component for decompression Sayer et al., 2008; Denoble et al., 2009; Sayer and monitoring. The accurate conversion of pressure Brown, 2010; Kuch et al., 2012; Vacchi et al., 2012). measured to depth displayed is not possible without A general conclusion from the present study is that the concomitant accurate determination of salinity using a non-calibrated dive computer to give an and temperature. The frequency of data storage will absolute depth reading cannot be recommended. always be compromised by factors related to the size Measuring relative heights or depth ranges (Sayer and cost of the computers. If the diver is using the and Brown, 2010) may have more credibility, but computer depth display to compute decompression should still be confirmed with physical measure- obligations using decompression tables, then the ment. Although working at altitude, Buzzacott and results from the present study show that, with the Ruehle (2009) acknowledged the difficulty of majority of depth estimates being in the ±1m range, obtaining a true water depth using standard dive dive computers should be accurate enough for most computers and resorted to physical measurement table depth intervals (usually 2m or 3m). methods (tape measures) to obtain the nominal In contrast, caution is recommended for the use water depth. of dive computers as depth measurement tools in10 Vol 31, No 1, 2012scientific study or underwater surveying. If there is easyUp/file/instructions/IB_ArchimedeII_2008_en.pdfsufficient knowledge of the salinity of the water the [last accessed 29 July 2012]. Cressi Sub. (n.d. b). Cressi Edy User’s Manual. Genova, Italy:computers are being used in and the salinity they Cressi Sub, 232pp. Accessed from www.cressi.it/easyUp/are calibrated to, then accuracy levels of ±1% could file/instructions/IB_Edy_2008_en.pdf [last accessedor should be expected. The acceptability of that 29 July 2012].level of error will depend on the application of the Denoble PJ, Dunford R, Sayer MDJ, Pollock NW, Nord D anddepth measurements. Vann RD. (2009). Predicted probability of decompression From the point of view of forensic examination sickness in 159 treated cases with documented dive pro- files. Undersea and Hyperbaric Medicine 36: 253–254.of diving computers, both depth and temperature European Standard (2000). EN 13319: 2000 Diving accesso-records may need to be treated with some caution. ries. Depth gauges and combined depth and time measur-Where available the unit should also be calibrated ing devices. Functional and safety requirements, testagainst known pressures and water temperatures ­methods. Brussels: European Committee for Standarization.if those metrics are important to the investigation. Huggins KE. (2012). Dive computer considerations. In: Blogg SL, Lang MA and Møllerløkken A. (eds.). Proceed-Overall in this study, temperature measurement ings of the Validation of Dive Computers Workshop. August 24,and display were highly variable in the units exam- 2011. European Underwater and Baromedical Societyined, and it is concluded that dive computers Symposium, Gdansk. Trondheim: Norwegian Universityshould not be employed to measure water tempera- of Science and Technology, 19–28.tures for scientific study. Kuch B, Buttazzo G, Azzopardi E, Sayer MDJ and Sieber A. (2012). GPS diving computer for underwater tracking and mapping. Underwater Technology 30: 189–194. Mares. (2005). Mares Nemo Manual. 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