forum.heinrichsweikamp.com

Hi Guys,

Running some checks between the OSTC simulator and GUE's Deco Planner.

Can't seem to get the same result on both and would like to ask if you could please help me figure out what's making the difference (not implying anything wrong. I'm sure it's interpretation and settings)

I have been able to replicate the Deco Planner outcome in a separate software so I would like to understand how the OSTC display's its results.

Deco Planner settings and outcome:

Depth 45
Time 21

Bottom Gas Air
Deco gas EAN65 (from 12) (which is what's left on my pony right now)

last stop 3m

GF 30/80

Descent 20m/min (I'm sure the here is one of the problems)
Ascent 10m/min

mBAR 983 (trying to mimic the OSTC reading)

Depth -Time- Gas
45 - 21 - 21
21 - 1
18 - 1
15 - 1
12 - 2 - 65
9 - 2
6 - 4
3 - 7

OSTC simulator result:

EAN^% set from 12m

mBAR 983 (it was moving between 982 and 983)

Depth Time Gas
45 - 21 - 21
21 - 2
15 - 3
12 - 2 - 65
9 - 3
6 - 4
3 - 10


I run the OSTC simulator two or three times and the result came different a
bit different on the 15m stop (4min rather than 3min) but that may not be a big deal if it is reading the ambient pressure to make the simulation.

Your help is appreciated.

Different algorithms will give diffent results no matter what you do.

How about playing with the gradient factors. Maybe increasing the low and high values to allow you to sail closer to the M value, might shorten your stops a bit.

CF32: GF low value
CF33: GF high value

Regthing Wrote:
-------------------------------------------------------
> Different algorithms will give diffent results no
> matter what you do.
>
> How about playing with the gradient factors. Maybe
> increasing the low and high values to allow you to
> sail closer to the M value, might shorten your
> stops a bit.
>
> CF32: GF low value
> CF33: GF high value

Hi Scott,

I respectfully disagree. If you take a look at this page:

http://www.heinrichsweikamp.com/en/ostc_mk2/

it clearly states that:

"What this OSTC Mk.2 dive computer is:
An experimental platform for all experienced divers who are interested in the theory of diving and who value maximum transparency and individual adaptabily ."


and ore importantly:

"Which mathematical model does the computer use for calculating decompression, and why can't can't I see and follow it exactly?"

I have tried reading the OSTC code, believe me it makes no sense to me and therefore why I'm asking the question on the forum.

However, I have compared at least 4 different decompression software running ZHL-16 GF. They all give me the same outcome. One stop may be differ for one minute or so but overall they are the same.Differences in those programs come from stop calculations as some calculate stops in seconds some round up to whole minutes. Deco planner, Gap, JDiveLog (MVplan), JDeco and "XS for Windows" provide the same outcome using the same combination of gases, depth, bottom times and GF the OSTC simulator doesn't.

The OSTC is set to ZHL GF with the same settings as the other software so it should provide the same outcome.

It is more conservative which is OK and it may be that the stop shown in the simulator includes the ascent or something like that. However, I still want to understand where the difference comes from.

Best regards,

D

from changelog Firmware 1.71
[pre]
"Decosum" changed to "TTS" (Time to Surface)
[/pre]
yes, it's the ascent-time + all-deco-times

Chilihead Wrote:
-------------------------------------------------------
> from changelog Firmware 1.71
>
> "Decosum" changed to "TTS" (Time to Surface)
>
> yes, it's the ascent-time + all-deco-times


Thanks mate,

This simply means that my mate with the X1 and my other mate with the Predator and I can run the same profiles and come out together.

D

try to change the saturation/desaturation to 100%. this should provide the desired and comparable outcome!

regards
ewatsch

ewatsch Wrote:
-------------------------------------------------------
> try to change the saturation/desaturation to 100%.
> this should provide the desired and comparable
> outcome!
>
> regards
> ewatsch


Thanks mate,

I'll try it. Although I thought that the sat and de sat CF's only affected plain ZHL calcs and had nothing to do with the Gradient Factor ones.

The other thing is consistency. You can run the simulator 10 dimes and obtain 10 different (but similar) outcomes. Is it assuming repetitive dives? if so how do you clear it?

D

Does the OSTC assume instant descent to depth by any chance?
Try setting Decoplanner descent to 1000m/min or whatever it maxes out at maybe?

Lee

Thanks Lee,

I'll try that as well.

As per ewatsch's recommendation I did change the sat/desat settings and tried a couple of times.

Although there are a number of posts that state that the sat/desat CF's do not affect the deco calcs when using the GF algorithm on the actual dive, changing the CF's did change the outcome provided by the simulator.

Matthias would you be so kind to shed some light into this?

How do we need to set the OSTC in to obtain results consistent with other ZHL GF decompression Softwares?

Also, why does the simulator keeps changing the outcomes? You run it 10 times and get 10 different outcomes?

Thanks,

D

Hello,

I mean OSCT use ZHL16C (for computer, so more conservative) and you configure decoplanner with ZHL16B (for table)

an extract from decoplanner manual:
[pre]
Table Selection (alt T)
This allows access to changing which of the Algorithms is used in the Deco
Planner software - currently 2 of the Bühlmann’s systems are used ZHL16B and
ZHL16C. ZHL16B is intended for generation of tables and dive profiles, ZHL16C
is intended for minute by minute calculations such as those computed by a in
water dive computer. Both models have been included as educational tools. For
most dive planning it is recommended the user uses ZHL-16B.
[/pre]

Change the Decoplanner's settings.

Regards
Servan

Hi Servan,

Yes agreed, However, the only difference in the implementations between the B and the C are the M values of certain compartments. This has a knock on effect on "a" and ""b" values and thus GF. The implication is that you will not be able to ascend as shallow and may need to stay a bit longer at the stops. I get that.

My main problem is that the simulator can give you 5 different answers if you run it in five different occasions. I have tried even to reset the pc between each run to see if I can get any consistency. I can't.

The explanation could be as simple as the specific pressure taken at the beginning of the simulation. But until its clear...

I just made a simulation and it is asking for :

(2min)21m, ((zero) 18m, (4min)15m, (1min)12m, (4min)9m (4min)6m and (10m)3m.

Second run (10 seconds later)

(1min)21, (1min)18m (3min)15m, (2min)12, (3min)9, (4min)6m, (not shown)3m

The other issue is the length of the stop it does add substantial amount of time to each stop (up to 4 minutes in certain deep stops vs one minute on the desktop software.

Again, it would be nice to understand why. It could be as simple as rounding on the display of the deco profile...

D

D

Hi dmainou,

I recognized the same. Same deco algorithms but different results.
No clue why, BUT I found out why the simulation of the same dive gives you different results.
The ostc calcs the second simulation as a repetition dive, the 3rd dive as a repetition of the second...
So this is what I do to simulate:
Before simulating, go to "reset Menu" than "reset decodata", confirm. you are done and get always the same results.
cheers Thom

Hi Thom,

Have you tried doing that with the current stable version?

It doesn't seem to work for me. I have tried that before and it's ever written up there.

Thanks mate

Yepp,
I'm currently running 1.7.2 on my ostc.
I've tried it with 1.7 and I think, I'll go back to 1.7.
I've to say, I do't understand the decomodell what is running on the ostc.
ALL my other decoprogramms (GAP, ideco, GUE decoplan and v-planner) generate similar decos.Bu the ostc generates significant longer decos. For example:
Today I did an easy dive on Nitrox 32. My Buddy used a suuto Vytec set to air.
After leaving the bottom an ascending we both had 2 minutes bottomtime left.
My ostc is set to GF 20/90 on Nitrox 32! And the vytec is not knowen as an aggressive computer.
So here's my solution: Dives (lakes) on Nitrox 32 I switch to the Gauge Mode an calculate by 90 rule and minimal deco.
Dives on 32 Nitrox in Caves (jojo) Zhl 16 without GF Faktors
Dives on Trimix: GF 10 / 85

So that works for me

Cheers
thom

H Thom,

I have read as much as I can about the different models. Can't read German so haven't read Buhlmann's book.

Also can't program assembler so can't actually understand what the OSTC is doing. (I've tried)

However, the simulator does mimic the expected curve. Although, as you point out, with longer stops.

I would really like to understand why. I don't mind conservatism. The last thing I want to do is get bent. I however would like to understand the differences between computers all claiming to run plain ZHL +GF.

In theory the equation is the same...

D

OK figured it out.

To get "semi" consistent results on the OSTC you need to exit all menus between simulations. Did 20 runs and averaged them to get the average profile. (The crucial bit is exiting all menus before running the simulator again)

Then went to decoplanner and set as many parameters as possible in line with the OSTC including one called "depth safety factor" which uses the depth multiplied by 1.03 + 1 meter (close enough to the +1 meter on the OSTC default setting)

The outcome is basically in line with decoplanner. On the OSTC the last stop is two minutes longer and one of the deeper stops is, on some runs, a minute longer but no big deviations.

Thanks for the input guys

D