On the reliability of dive computer generated run-times 07.02.2022, Part V

Abstract

On the reliability of dive computer generated run-times
07.02.2022, Part V
Here, in Part V, we checked the ZH-L16C implementation of one SHEARWATER® dive computer with the original source, the air diving table ZH-86 from A. A. Bühlmann [2] along selected table entries as well with a freeware/shareware implementation [1], [3] as a 2nd. benchmark.

Conclusion: the manufacturers claims on using the ZH-L16C model could be verified: within the limited precision of dive computers / depth gauges / dive watches there is
reasonable agreement for operational air-diving in the recreational domain.

Full text

1
On the reliability of dive computer
generated run-times
07.02.2022, Part V
Miri Rosenblat, TAU
Nurit Vered, Technion Haifa
Yael Eisenstein &
Albi Salm, SubMarineConsulting
DOI:

2
On the reliability of dive computer
generated run-times, Part V
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
and per part IV, check of a DCIEM implementation, to be published asap!
Here, in Part V, we checked the ZH-L16C implementation of one
SHEARWATER® dive computer with the original source, the air diving table
ZH-86 from A. A. Bühlmann [2] along selected table entries as well with a
freeware/shareware implementation [1], [3] as a 2nd. benchmark.
Conclusion: the manufacturers claims on using the ZH-L16C model could be
verified: within the limited precision of dive computers / depth gauges / dive
watches there is reasonable agreement for operational air-diving in the
recreational domain.
Methods: slides # 3  5
Results: slides # 6  14
Discussion, Conclusion & Recommendations: slides # 15 & 16
References: slides # 17  21

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On the reliability of dive computer
generated run-times, Part V
Methods (1):
Comparison of the run-times/TTS from the original ZH-86 air table ([1],
slides # 17  19) with the calculated run-times by DIVE ([1] & [3]) and the
dive-computer generated run-times, obtained in (surface-)planning mode set
to „air“, pls. cf. slides # 6  14.
The tested dive computer is the SHEARWATER PERDIX ® with the latest
firmware V87 from 2021-11-01, put to air in „OC Tec“ mode:
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; the „NDL
Planner“ runs from 12  45 m.

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On the reliability of dive computer
generated run-times, Part V
Methods (2):
The ZH-86 entries are taken from the book [2] & slides # 17 19,
DIVE Version 3_11 are screen copies, the upper part showing unmodified
values, i.e. GF = 1.0, the lower part with the GF. The required configurations
to adapt for the settings in the PERDIX are on slide # 20. The Shearwater
„OC Deco Planner“ values are digital stills. „OC“ here stands for „Open
Circuit“, which is normally used in air diving (in contrast to „CC“, closed
circuit, a rebreathing device).
Tables Ia & Ib (slide # 6 & 7) 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 # 6 – 14) 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 DIVE 3_11 and a digital still from the dive
computer.

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On the reliability of dive computer
generated run-times, Part V
Methods (3):
The dive computer is set to „OC Tec“ mode which allows for
configuration of the gradient factors GF: these have been set to
GF High = GF Low = 0.99 to allow for, at least a limited, comparability with
the original ZH-86 values from the printed air diving tables (GF Hi = GF Lo =
1.00 or 100 %). The comparability is limited because the ZH-86 tables are
calculated with the ZH-L16B set, whereas the dive computer is set to use
the ZH-L16C values. As per [2], p. 157, the –B set is for table calculations
whereas the –C set should be used for dive computers. Thus the ZH-86
tables could serve as a benchmark with nearly similar TTS / stop times per
stage in comparison to any dive computers calculations using the –C set.

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On the reliability of dive computer
generated run-times, Part V
Results (1):
Table Ia: comparison of the NDL, the „no-decompression limits“:
depth
[m] NDL [min]
ZH-L16C with
GF Hi = GF Lo
= 0.99
NDL [min]
PERDIX
9 720 -
12 175 165
15 86 86
18 57 57
21 39 41
24 29 31
27 22 23
30 16 19
33 13 15

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On the reliability of dive computer
generated run-times, Part V
Results (2):
Table Ib: comparison of the NDL, the „no-decompression limits“:
N.B.: the “OC Deco Planner” is not accessible in “AIR” mode, but the “NDL
Planner” is.
depth
[m] NDL [min]
ZH-L16C with
GF Hi = GF Lo
= 0.99
NDL [min]
PERDIX
36 11 13
39 9 12
42 8 10
45 7 9
48 5 -

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On the reliability of dive computer
generated run-times, Part V
Results (3):
comparison of the schedule: 18 m, 60 min bottom time:
Rem.: the „TTS“ , the „time-to-surface“ is defined as:
sum of all stop times + (bottom depth / ascent speed);
run, run time = bottom time + TTS

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On the reliability of dive computer
generated run-times, Part V
Results (4):
comparison of the schedule: 18 m, 180 min bottom time:

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On the reliability of dive computer
generated run-times, Part V
Results (5):
comparison of the schedule: 30 m, 120 min bottom time:

11
On the reliability of dive computer
generated run-times, Part V
Results (6):
comparison of the schedule: 33 m, 60 min bottom time:

12
On the reliability of dive computer
generated run-times, Part V
Results (7):
comparison of the schedule: 42 m, 25 min bottom time:

13
On the reliability of dive computer
generated run-times, Part V
Results (8):
comparison of the schedule: 45 m, 30 min bottom time:

14
On the reliability of dive computer
generated run-times, Part V
Results (9):
comparison of the schedule: 51 m, 30 min bottom time:

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On the reliability of dive computer
generated run-times, Part V
Discussion:
Tables Ia & Ib show a good agreement between the calculated ZH-86 table
NDL and the dive computer generated values.
The other schedules agree as well. The delta-times of 1 min +/- 0.5 are
well within the precision of used equipment for practical diving.
Thus these deviations are negligible for recreational air-diving and do not
imply any safety/security hazards.
Conclusion:
That is, the manufacturers claims of using the ZH-L16C set with
the GFs = 0.99 could be fully verified. This means as well, that considerations
concerning the risk of recreational air diving put forth by Bühlmann
([2], pp. 158 & 164 - 178) are valid here for the tested dive computer with
these air-diving configurations as well.

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On the reliability of dive computer
generated run-times, Part V
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 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

17
Comparison with ZH-86 table:
Source: [65], pp. 227; i.e.: http://www.divetable.eu/BOOKS/65.pdf;
the yellow display is ours: "Tauchmedizin",
Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter), P. Nussberger;
5. Auflage in 2002, Springer, ISBN 3-540-42979-4

18
Comparison with ZH-86 table:
Source: [65], pp. 227; i.e.: http://www.divetable.eu/BOOKS/65.pdf;
the yellow display is ours: "Tauchmedizin",
Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter), P. Nussberger;
5. Auflage in 2002, Springer, ISBN 3-540-42979-4

19
Comparison with ZH-86 table:
Source: [65], pp. 227; i.e.: http://www.divetable.eu/BOOKS/65.pdf;
the yellow display is ours: "Tauchmedizin",
Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter), P. Nussberger;
5. Auflage in 2002, Springer, ISBN 3-540-42979-4

20
Additional Settings required for DIVE V 3_11 to
reflect the special ZH-L16C calculations within the
„OC Deco Planner“ (slides # 6  14 and [3]):
Source: https://www.divetable.info/beta/D3_11.exe
„NC“: selection of the ZH-L16C set („1“, = default)
„AR“: ascent rate: 10 m / min
„DI“: for water density 1020.00 kg/m3
„L“: for ambient pressure at start of dive
fraction of oxygen fO2, respiratory quotient Rq &
water temperature are set to the software defaults
To simulate the „OC Tec“ settings in the Shearwater
PERDIX ®:
„GF“: for Gradient Factors High = Low = 0.99
used bottom times for planning: - 0.5 or - 1.0 min to
accomodate for the computers descent rate of 18 m / min;
since DIVE uses, as usual in table calculations, per
default an instantaneous descent.

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On the reliability of dive computer
generated run-times, Part V
References:
[1] Vered N., Rosenblat M., Salm, A. (2021) Synopsis & Fact Sheet
DIVE Version 3_11,
DOI: https://dx.doi.org/10.13140/RG.2.2.17024.56326
[2]  [65] Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter),
P. Nussberger (5. Auflage in 2002) Tauchmedizin, Springer, ISBN 3-540-
42979-4
[3] Rosenblat M., Vered N., Eisenstein Y.; Salm A. (2022) Recovery of
selected ZH-86 air-diving schedules via a decompression shareware
DOI: 10.13140/RG.2.2.34235.13609
The dive computer manufacturers homepage:
https://www.shearwater.com/