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Abstract

On the reliability of dive computer generated run-times, 11.01.2022, Part II Abstract: Here, in Part II, we checked a simple run-time (bottom depth 45 m / bottom time 30 min on air) with the 3 different dive computers in comparison with the original source, the ZH-86 from A.A. Bühlmann and two free-ware desktop deco-programs. Results: there is substantial variation in the TTS: these variations could not be substantiated with the dive computer manufacturers claims. The original source claims to use a „safety sur-charge“: this as well could not be verified for the choosen particular dive schedule here.
1
On the reliability of dive computer
generated run-times
11.01.2022, Part II
Miri Rosenblat, TAU
Nurit Vered, Technion Haifa
Yael Eisenstein &
Albi Salm, SubMarineConsulting
DOI: t.b.d.
2
On the reliability of dive computer
generated run-times, Part II
Abstract:
Idea: as per part I, DOI: 10.13140/RG.2.2.16260.65929
Here, in Part II, we checked a simple run-time @ bottom depth 45 m / bottom
time 30 min. on air with the Scubapro/UWATEC ® Galileo G2 computer, the
Scubapro/UWATEC ® Aladin[2] and the RATIO iX3M DEEP from Dive
System ® in comparison with the original source, the ZH-86 from A.A.
Bühlmann [2] and two free-ware desktop deco-programs, DIVE Version 3_11
[1] and Subsurface 5.0.5.
Methods:
Comparison of the TTS from the original ZH-86 ([2] [65]) with the dive-
computer generated run-times, obtained in (surface-)planning mode, pls. cf.
slides # 6 to 10, and with the cited software products (Ref. [1] and all the
references therein).
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On the reliability of dive computer
generated run-times, Part II
Results:
there is substantial variation in the TTS, pls. cf. table on slide # 4!
These variations could not be substantiated with the dive computer
manufacturers claims, pls. cf. the manuals of these products.
The original source claims to use a „safety sur-charge“: this as well could not
be verified for the choosen particular dive schedule here.
Discussion / Conclusion:
pls. cf. slides # 11 & 12
Recommendation:
slide # 13
References:
slide # 14
4
On the reliability of dive computer
generated run-times, Part II
Focus here is on the TTS only, the time-to-surface, i.e.
sum of all stop times + (bottom depth/ascent speed):
Source: TTS [min] remark
Subsurface 46 default, slide # 7
ZH-86 [65] 49 original table, slide # 5
DIVE 3_11 49 default, slide # 7
RATIO iX3M 50 default (GF = 0.93), slide # 6
Subsurface 52 Safety Factor, slide # 8
DIVE 3_11 54 Safety Factor, slide # 8
Subsurface 54 Gradient Factors, slide # 9
DIVE 3_11 55 Gradient Factors, slide # 9
Aladin[2] 67 default, slide # 6
Galileo G2 69 default, slide # 6
5
Comparison with ZH-86 Table:
Source: [65], p. 227; i.e.:
http://www.divetable.eu/BOOKS/65.pdf
"Tauchmedizin", Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter),
P. Nussberger; 5. Auflage in 2002, Springer, ISBN 3-540-42979-4
6
45 m, 30 min:
7
default setting, no Bühlmann Safety Factor,
no Gradient-Factors set:
DIVE V3_11:
Subsurface 5.0.5.:
8
with Bühlmann Safety Factor,
i.e.: 45 * 1.03 +1.0 = 47.35, no Gradient-Factors
DIVE V3_11:
Subsurface 5.0.5.:
9
no Bühlmann Safety Factor,
Gradient-Factors set: GF High = 0.93, GF Low = 0.93
(as per default setting in RATIO iX3M DEEP)
DIVE V3_11:
Subsurface 5.0.5.:
10
Additional Settings required for DIVE V 3_11 to
reflect the special ZH-86 calculations for the printed
air tables (slide # 5) :
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 (45 - 12) / 3 = 11 m / min
„DI“: for water density 1020.
„L“: for ambient pressure at start of dive
The Scubapro/UWATEC computers were @ default.
To simulate the default settings on the RATIO iX3M
DEEP ®, (PS = 0, ALGORITHMUS = BUL)
„GF“: for Gradient Factors High & Low 0.93
as per manual OS 4.0.77, p.29:
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On the reliability of dive computer
generated run-times, Part II
Discussion (1):
The TTS table (slide # 4) reveals very quickly:
The Scubapro/UWATEC computers deviate by as much as ca. 20 min,
ie. ca. 40 % (!) from the original TTS.
The claimed gradient factors in the RATIO computer could not really be
substantiated; the manufacturers claimed use of the ZH-L 16 B set (pls. cf.
slide # 10) instead of the „C“ set, which is intended for dive-computers ([2],
p. 157), could be questioned.
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On the reliability of dive computer
generated run-times, Part II
Discussion (2):
Both software products, i.e. DIVE and Subsurface, follow each other and
the original ZH-86 very closely. This, by no means implies, that these
results should be considered perfect or even sound for diving, as this
schedule is basically un-validated via the required 100 to 200 man-dives
(or women-dives).
But it shows clearly, that despite the used very different software
technologies (FTN90 or FTN66 vs. C, 64 Bit vs. 8 Bit, CLI vs. GUI(*) etc.)
and the different development processes (closed shops vs. open source)
the original ideas/algorithm could be solidly and reliably recovered.
For this particular schedule, it seems that the ZH-86 has neglected the
claimed safety factor as per „2.“ of [2] on p. 165, or the claimed ascent
speed of 10 m / min (loc. cit.) was not used: this particular TTS should be
clearly around 58 min instead of 49 min!
(*); CLI: command line interface, GUI: graphical user interface
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On the reliability of dive computer
generated run-times, Part II
Recommendations:
As per Part I, DOI: 10.13140/RG.2.2.16260.65929 :
Dive Computer Manufacturers should:
reveal the used set of constants (i.e. these constants used at run-time!)
as well, like in any other desktop deco-software:
the used water density, ascent rates, respiratory coefficient, etc. … and:
implement quality assurance procedures
agree on a set of benchmarks, standardized for all players in the market
to achieve a transparent comparability
and / or a public code-review
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On the reliability of dive computer
generated run-times, Part II
References:
[1] Nurit Vered, Miri Rosenblat; Salm, Albi (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
Subsurface is available @: https://subsurface-divelog.org/
The dive computer manufacturers sites:
https://www.scubapro.com/
https://www.ratio-computers.com/
... As the user-interfaces for the Scubapro G2 and the G2 TEK are nearly the same, the descriptions in the Refs. [1] & [2] are still valid. ...
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On the reliability of dive computer generated run-times, Part VIII: G2 TEK Abstract: Here, in Part VIII, we performed some basic comparisons with the highly topical SCUBAPRO / Uwatec mix-gas dive computer Galileo 2 TEK / G2 TEK along the SHEARWATER PERDIX. Both have been set to a standard perfusion model ZH-L 16 without and as well with gradient factors.
... i.e. the change, the error that is, of P t is found in its total differential: dP t (t) = (δP/δp amb ) * dp amb + (δP/δf Inert ) * df Inert + (δP/δt) * dt (2) by neglecting 2nd. order variations and errors/variations in time and other variables, a Taylor expansion gives the variation of P t (t) and reduces approximately to: ...
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On the reliability of dive computer generated run-times, Part VI: Error Propagation Abstract: Here, in Part VI, we only point out to the law of error propagation. During the previous 5 parts ([1] to [5] and all the references therein), we observed by some of the dive computer manufacturers deviations from documented algorithms/decompression models. Additionally to these software-driven variations are those, driven by hardware and the statistical errors by measuring ambient pressure, time, temperature and the inertgas contents of the breathed gas-mix.
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Here, in Part VII, we performed an altitude test, i.e. the simulation of diving in a mountain lake. During the previous parts I to VI ([1] to [6] and all the references therein), we observed by some of the dive computer manufacturers deviations from documented algorithms/decompression models with simulated dives on sea-level (SL), whereas Part VII covers a test at reduced ambient pressure of ca. 0.8 Bar, i.e. a mountain lake at a ca. altitude of 2.000 m above SL.
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