On the reliability of dive computer generated run-times (22.02.2022) Part IV

Abstract

On the reliability of dive computer generated run-times (22.02.2022) Part IV

Here, in Part IV, we checked the DCIEM implementation of one SHEARWATER® dive computer with the original source, the air diving table from the DCIEM Diving Manual [1] along selected table entries.

Conclusion: the manufacturers claims on using the DCIEM model could be verified only partially, since deviations with longer bottom times surfaced.

Full text

1
On the reliability of dive computer
generated run-times
22.02.2022, Part IV
Miri Rosenblat, TAU
Nurit Vered, Technion Haifa
Yael Eisenstein &
Albi Salm, SubMarineConsulting
DOI:

2
On the reliability of dive computer
generated run-times, Part IV
Abstract:
Idea: as per part I, DOI: 10.13140/RG.2.2.16260.65929
and per part II, DOI: 10.13140/RG.2.2.11343.41126
and per part III, DOI: 10.13140/RG.2.2.21973.50405
Here, in Part IV, we checked the DCIEM implementation of one
SHEARWATER® dive computer with the original source, the air diving table
from the DCIEM Diving Manual [1] along selected table entries.
Conclusion: the manufacturers claims on using the DCIEM model could be
verified only partially, since deviations with longer bottom times surfaced.
Methods: slides # 3 & 4
Results: slides # 5  18
Discussion, Conclusion & Recommendations: slides # 19 - 21
References: slides # 22 & 23
Attachment: slide # 24

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On the reliability of dive computer
generated run-times, Part IV
Methods (1):
Comparison of the run-times/TTS from the original DCIEM air table ([1],
slide # 22) with the dive-computer generated run-times, obtained in
(surface-)planning mode set to „air“, pls. cf. slides # 5  18.
The used dive computer is one SHEARWATER PERDIX ® with the latest
firmware V87 from 2021-11-01 with a DCIEM unlock code:
The tools to simulate the dive schedules are the so-called „Deco Planner“ and
the „NDL Planner“. The possible entries in the „Deco Planner“ are:
for bottom depth 3  150 m, and bottom time 5  180 min.

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On the reliability of dive computer
generated run-times, Part IV
Methods (2):
The DCIEM entries are taken from the diving manual ([1] & slide # 22),
the Shearwater Deco Planner values are digital stills:
Tables Ia & Ib (slide # 5 & 6) compare the various NDL in minutes from
9  48 m bottom depth. The NDL is a „no-decompression-limit“,
aka „no-stop-limit“ for a diver to surface from a dive without decompression
stops.
The slides in the results-section (slides # 7 – 18) show the schedules with
bottom depth, bottom time and the stop times for the 3, 6, 9, 12, … m stops,
each with a clip from the DCIEM tables and a digital still from the dive
computer, set to „Air“, „DCIEM“ & intermediate water density (EN13319).

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On the reliability of dive computer
generated run-times, Part IV
Results (1):
Table Ia: comparison of the NDL, the „no-decompression limits“:
depth
[m] NDL
DCIEM
[min]
NDL
PERDIX
[min]
9 300 -
12 150 145
15 75 75
18 50 50
21 35 35
24 25 26
27 20 21
30 15 16
33 12 12

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On the reliability of dive computer
generated run-times, Part IV
Results (2):
Table Ib: comparison of the NDL, the „no-decompression limits“:
depth
[m] NDL
DCIEM
[min]
NDL
PERDIX
[min]
36 10 10
39 8 8
42 7 7
45 7 7
48 6 -

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On the reliability of dive computer
generated run-times, Part IV
Results (3):
comparison of the schedule: 18 m, 180 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (4):
comparison of the schedule: 21 m, 180 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (5):
comparison of the schedule: 24 m, 150 min bottom time:
With: “SeaLvl”, “SALT”: 9 m / - min, 6 m / 44’, 3 m / 112’, ΣDeco: 156‘

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On the reliability of dive computer
generated run-times, Part IV
Results (6):
comparison of the schedule: 30 m, 105 min bottom time:
With: “SeaLvl”, “SALT”: 12 m/- min, 9 m / 10’, 6 m / 41’, 3 m / 106’, ΣDeco: 157‘

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On the reliability of dive computer
generated run-times, Part IV
Results (7):
comparison of the schedule: 33 m, 60 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (8):
comparison of the schedule: 42 m, 25 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (9):
comparison of the schedule: 45 m, 30 min bottom time:
pls. cf. the attachment, slide # 24 for another comparison of this schedule

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On the reliability of dive computer
generated run-times, Part IV
Results (10):
comparison of the schedule: 51 m, 30 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (11):
comparison of the schedule: 51 m, 70 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (12):
comparison of the schedule: 60 m, 15 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (13):
comparison of the schedule: 60 m, 50 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Results (14):
comparison of the schedule: 72 m, 40 min bottom time:

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On the reliability of dive computer
generated run-times, Part IV
Discussion & Conclusion:
Tables Ia & Ib show a good agreement between the printed DCIEM table NDL
and the dive computer generated values. Schedules with short bottom times
agree as well within the limited precision of gauges used for practical diving.
With bottom times becoming longer, sometimes the deepest stops are
missing (slide # 7, 9, 10, 11) or are modified in depth (slide # 17, 18) and the
shallow stop times are modified, with the tendency of increasing the stop
times in comparison to the printed entries @ 3 and 6 m to compensate the
TTS for the deepest missing or modified stops. Setting the water density to
„Fresh“ will loose even more TTS, setting it to „Salt“ increases the TTS
beyond the DCIEM table-values for the next step / next longer BT.
Thus, series of identical repetitive dives with various lengths of surface
intervalls (SI) would reveal more details of this DCIEM implementation.
But this is clearly beyond the scope of the Perdix Planner (Manual, Rev . E, p.
57), limited to simple square / box-profiles and no SI.

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On the reliability of dive computer
generated run-times, Part IV
Discussion & Conclusion:
In the DCIEM diving manual [1] there is in chapter 7, pp. 1-26  1-29, the
procedure for so-called „multi-level“ dives. These are dives typically done by
recreational divers, not staying the complete bottom time on one depth, but
instead staying varying times at different depths. Since multi-level dives also
can not be handled with the dive computers planning tools, a test on the
compliance with these procedures would be a completely new line of
research.
Professional use is based usually on only one dive a day and with the current
data at hand the sole usage, i.e. the dive computer being a single source for a
dive plan, for an occupational group of divers subjected to occupational and
legal regulations, is not recommended: control & supervision of (table-guided)
decompression from top-side is non-negotiable.
This even more so when considering that HELIOX mixes (only O2 & Helium)
are typical for professional use: presently this is also not implemented
in the Shearwater-DCIEM software.

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On the reliability of dive computer
generated run-times, Part IV
Recommendations:
As per Part I, DOI: 10.13140/RG.2.2.16260.65929 and / or
part II: DOI: 10.13140/RG.2.2.11343.41126
and / or part III: DOI: 10.13140/RG.2.2.21973.50405
To achieve a transparency for the customer (the diver) and a fair
comparability between the dive computers, Dive Computer Manufacturers
should:
reveal the used set of constants (i.e. those constants used at run-time!)
as well, like in any other desktop decompression-software:
the used water temperature & density, ascent rates, respiratory coefficient,
ambient air pressure, transit times, etc. etc. … and:
implement quality assurance procedures
esp. after software/firmware update / patches
agree on a set of benchmarks, standardized for all players in the market
and / or a code-review, with the results to be published

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Comparison with the DCIEM table:
Source: [1], p 1B-5  1B-18 ; i.e.: http://www.divetable.eu/p125936.pdf;

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On the reliability of dive computer
generated run-times, Part IV
References:
[1] DCIEM Diving Manual, DCIEM No. 86-R-35: Part 1 AIR Diving Tables and
Procedures, Part 2 Helium-Oxygen Surface-Suppplied Decompression
Procedures and Tables; Defense and Civil Institute of Environmental
Medicine, Canada
The dive computer manufacturers homepage:
https://www.shearwater.com/
DCIEM flyer:
https://www.shearwater.com/wp-content/uploads/2021/07/DCIEM-Manual-
Metric-Web-1.pdf

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For a comparison w. slide # 13, the 45 m/30‘ schedule,
taken from: DIVING DECOMPRESSION COMPUTER (XDC-2)
VALIDATION DIVES. 36 - 54 msw, F PHASE I –
PRELIMINARY RESULTS, p. A-7, tested with 6 man-dives:
XDC-2: pneumatic dive computer
USN: United States Navy 1958,
RN: Royal Navy,
FN: French Navy;