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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