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2
On the reliability of dive computer
generated run-times, Part III
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
Here, in Part III, we checked 3 simple run-times with bottom depth 18 m / 60
min, 33 m / 60 min & 51 m / 30 min bottom times on air with the RATIO iX3M
DEEP from Dive System® in comparison with the original source, the ZH-86
from A.A. Bühlmann [2] and, DIVE Version 3_11 [1] & [3].
Conclusion: the manufacturers claims on using the ZH-L16B set of
coefficients with a certain set of pre-defined gradient factors could not be
verified.
Methods: slide # 3 & 4
Results: slide # 5 & 6
Discussion & Recommendations: slide # 7 & 8
Data: slides # 9 13
References: slide # 14
3
On the reliability of dive computer
generated run-times, Part III
Methods (1):
Comparison of the run-times/TTS from the original ZH-86 air table ([2] [65]
on slide # 12) with the dive-computer generated run-times, obtained in
(surface-)planning mode set to „air“, pls. cf. slides # 9 11, and with the cited
software product (Ref. [1] & [3] and all the references therein).
The used dive computer is the RATIO iX3M DEEP with the latest firmware
from 23.12.2021:
The tool to simulate run-times is the so-called „PLANER“ / „OC PLANER“.
The possible entries are: for bottom depth 3 180 m, and
bottom time 1 60 min. According to the user manual on p. 29 (pls. cf. refs.)
the used set of coefficients is the ZH-L16B; the default setting with
„PS: 0“ refers to a gradient factor pair of GF High = GF Low = 0.93 (i.e.
93 % of the tolerated supersaturation obtained from Bühlmanns original
values, that is GFs = 1.0, i.e.: 100 %) and with „PS: 3“ the GF pair should be
.75, i.e.: 75 % of Bühlmanns values.
4
On the reliability of dive computer
generated run-times, Part III
Methods (2):
The ZH-86 entries are taken from the book [2], the DIVE 3_11 values are
screen shots, the RATIO PLANER values are digital stills.
Tables I & II compare the TTS in minutes of the 3 schedules.
The TTS is the „time-to-surface“, usually defined as:
TTS = sum of all stop times + (bottom depth / ascent speed)
Table I (slide #5):
ZH-86 are the values from [2], these are compared with
DIVE 3_11, i.e. (gradient factors) GF High = GF Low = 1.0
(i.e.: 100 % of the tolerated supersaturation calculated with the original a- &
b-values of the ZH-L16B set from [2], p. 158)
RATIO, set „PS: 0“ with fresh- & seawater
Table II (slide #6):
(gradient factors) GF High = GF Low = 0.75
RATIO, set „PS: 3“ with fresh- & seawater
5
On the reliability of dive computer
generated run-times, Part III
schedule ZH-86 DIVE
3_11
GF = 1.0 / 1.0
GF High: 0.93 /
GF Low: 0.93 RATIO
PS: 0
fresh
RATIO
PS: 0
seawater
18 m /
60 min 7 7 11 4 5
33 m /
60 min 67 67 77 62 69
51 m /
30 min 66 66 72 66 69
Table I: TTS [min] of the 3 schedules
Results (1):
6
On the reliability of dive computer
generated run-times, Part III
schedule ZH-86 DIVE
3_11
GF = 1.0 / 1.0
GF High: 0.75 /
GF Low: 0.75 RATIO
PS: 3
fresh
RATIO
PS: 3
seawater
18 m /
60 min 7 7 23 15 17
33 m /
60 min 67 67 112 93 100
51 m /
30 min 66 66 107 90 97
Table II: TTS [min] of the 3 schedules
Results (2):
7
On the reliability of dive computer
generated run-times, Part III
Discussion:
Table I clearly indicates that the PS: 0 setting is neither equivalent to the
original ZH-86 values with GF High = GF Low = 1.0 (2nd. & 3rd. column)
nor to the more conservative values with the GF = 0.75 (4th. column in
green), be it for fresh- or seawater.
Table II indicates basically the same with the same trend:
the PS: 3 setting is not equivalent to the more conservative values with the
GF = 0.75 (4th. column in green), be it for fresh- or seawater.
That is, the customers claims of using this set of gradient factors (iX3M DEEP
user manual, p. 29) along with the set of ZH-L16B coefficients could not be
verified.
As the original source ([2], p. 156 & 158) states, that the “C” set should be
used for diver-carried computers due to enhanced conservativism, one could
question the manufacturers preselection on the “B” set (to be used only for
table calculations).
8
On the reliability of dive computer
generated run-times, Part III
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
To achieve a transparency for the customer (diver) and a fair comparability
between products, 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
13
Additional Settings required for DIVE V 3_11 to
reflect the special ZH-86 calculations for the printed
air tables (slide # 12 and [3]) :
Source: https://www.divetable.info/beta/D3_11.exe
„B“ : Buehlmann Depth Safety Factor
„NC“: selection of the ZH-L16B set („7“)
„AR“: ascent rate
„DI“: for water density 1020.
„L“: for ambient pressure at start of dive
fO2, respiratory quotient Rq &
water temperature set to default
To simulate the default settings on the RATIO iX3M
DEEP ®, (PS: 0, ALGORITHMUS: BUL)
„GF“: for Gradient Factors High = Low = 0.93,
resp. for PS: 3
GF Hi = GF Lo = 0.75;
as per manual OS 4.0.78, p.29:
14
On the reliability of dive computer
generated run-times, Part III
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.ratio-computers.com/
user manual:
https://www.ratio-computers.com/support/support4/manual/EN_iX3M_User_Manual.pdf