Desat interval bug in 1.90?

[rvs]

Dear HW,

The situation was: a 40m decompression air dive with 22:39 desaturation.
After the dive the surf. time, desat. & noFly interval are displayed OK.
But when I've made changes to neutral CF31 (show battery voltage/icon)
the surf. time, desat. & noFly unexpectedly shortened in about 7 hours
and displayed these wrong values until OSTC thinks that I'm
fully desaturated, where the actual desat. time should be 7 hours longer.
Suppose the surf. time value was corrupted by CF change process?

[JeanDo]

Hello Sergei,

What you are describing is undoubtedly a bug. Did anyone experienced is already ? Or is able to reproduce ?

Many Thanks,

[rvs]

Dear Jean-Dominique,

Can't still reproduce it again in full.
What I see while trying to replay it: when desat/nofly time is > 0,
after using simulator the surf. interval is always nullified and
the fully desaturated tissue graph is showed for a minute or so in surface mode.
During this minute after simulation, the desat. interval is not visible at all.
After this minute, the tissue graph is restored into the right state and desat. interval recalculated and showed correctly, but the surf. interval is started from zero and shows interval from the end of simulation, not the end of actual dive.

Will watch more, maybe I'll be able to reproduct what I've seen earlier in full.

[lmorais]

Hello ostc guys,

Sounds not to be the same problem, but about 12h after my last dive, ostc was no longer shown desat value on the screen, ostc indicates a desat value of 17:21h at the end of the dive. This means that the desat value are zero? Until that, desat value was decreased normally.

Was a swalow dive, max deep: 20m rt: 72min with nitrox 31, ostc running v1.95beta.

Could you explain that situation?

Best regards.

LMorais
Ostc 1079@Portugal

[nakatomi]

I just returned from a diving trip during which I did 23 dives over a period of 12 days (2 dives per day).
After every second dive of the day, at approx. 3pm, the desat time was shown to be around 24-27 hours.
However, early the next morning around 8am, the no-fly and desat counters had cleared already - apparently too early.

Several of the dives were a bit deeper as well (up to 52 meters), with a little more tissue loading, so a complete clearing of all tissues in 17 hours does not seem right at all.
All dives on air and Nitrox32 (the shallower ones).

I was using 1.95beta, if it matters any.

Also, this is weird as well, the new logbook would only hold 24 dives, on average around 55 minutes. I thought this was extended? My buddy had the same amount of dives in the logbook from this trip and he was diving 1.90 (the old logbook format).

[Solodiver]

24 dives seems quite much in my opionion, I'm just able to store about 5-7 dives (around 8hrs) using 1.95 and thought this is has been due to wrong divisors or some other "misconfigured" CF. But in the past I've seen much more so I agree that there might be something different in our understanding in the extension of the log book...

Thx,
Jan

[nakatomi]

I was under the impression that the new 64Bit logbook introduced in 1.91 would be able to store up to 40 hours (with the 10 second interval) while the old one would hold approx. 20 hours?
Nonetheless, my buddy with 1.90 has the exact same dives in his logbook as me, rollover at approx. 20 hours.

[heinrichsweikamp]

Hi,

Are CF20 to CF26 set to the same values in both computers?

Can you send us a binary dump of the logbook? In the Divinglog Downloader, select "Settings -> Write to binary".

Cheers,
Matthias

[JeanDo]

@Matthias

I did experience the same 20h limitation with the new format. All divisors being to default values.

Regards,

[rvs]

@Matthias, JeanDo

Desat. interval wrong: occurred again on 17.08.2011.
Conditions: FW V1.97beta.
Dive max.depth 43m, desaturation in logbook listed: 20:22.

after 08:10 surface OSTC lists Desat 5:41 in Surface mode.
08:10 + 05:41 != 20:22

Next, Surface int. 08:11 => Desat 05:34
Next, Surface int. 08:12 => Desat 05:33
Next, Surface int. 08:13 => Desat 05:31

Next, Surface int. 08:29 => Desat 05:31 (immediately after wakeup)
Next, Surface int. 08:30 => Desat 05:01
Next, Surface int. 08:31 => Desat 04:59
Next, Surface int. 08:32 => Desat 04:57

Next, Surface int. 08:42 => Desat 04:57
Next, Surface int. 08:43 => Desat 04:38
Next, Surface int. 08:44 => Desat 04:36

So we can see here - a part of desat. interval is lost during/after sleep mode.
Any ideas?

[rvs]

Perhaps the sleep mode interval is subtracted from desat. interval twice?
Take a look, after 15 min sleep Desat decremented to approx. 30 min,
after next 10 min sleep Desat decremented to 20 min... This could help to find a bug!

[lmorais]

Hello,

I'm going to dive tomorrow morning with ostc and i'll be staying alert with desat values vs sleeping mode.

I'm a bit worried about this, in case of multiple dives in same day, desat values must influence the next dive calculations.

Until tomorrow.

LM
OSTC 1079@Portugal

[tiefunten]

Yep, we should really try to fix this. It would be very nice to know if it is only a bug that prints something on the screen which is wrong but doesn't affect serious calculations (like the max. depth bug, which was not so important because the computer calculates using pressure), or if these wrong numbers are also used for calculations of multiple dives. But I can't dive at the moment...

Unfortunately neither Matthias nor JeanDo commented the last reports...!?

[lmorais]

Hello again,

Like i said on my last post, i´ve been following the evolution of desat values on ostc after my last dive, done yesterday morning.

Now after 12:20h after the dive, desat value shown on ostc is 1:05h, that means 13:25h total. At the end of the dive this value was 19:49h.

No fly value seams to be right, ends aprox. 11:50h after the dive.

At my home, air pressure is a bit lower than the pressure on the water surface 1012 vs 1016mbar.

Could you help us with this? It's only a display problem or the calculations are wrong?

Ostc MkII running v1.97 beta.

Best regards.

LMorais

[cparsons]

Yes, I would also like to know if this is just a display or a calculation problem?

I will shortly be doing a weeks diving with probably at least two dives a day so this could cause me serious problems if the desaturation calculations are not correct??

I currently have v1.97 beta loaded but does this problem also apply to v1.90?

I was prompted to buy the OSTC for this holiday, be a shame if I can't rely on it?

Regards

[heinrichsweikamp]

Hi,
The desat value is recalculated from the actual tissue load every minute in sleepmode. Even small changes of airpressure variation cause changes in this value. Decompression is not based on this value, it's always the computed tissue load that is taken into account.

Cris, when diving a week with 2-4 dives per day the difference between your actual tissue load and the calculated load in the OSTC after some days may be different. Add extra safety stops and wait at least 24h before flying.

We can change this bahavior to a more stable routine (By just counting the initial value to zero) or simply set the figure to 24h after every dive as other dive computers do. There are so many factors not taken into account for the desaturation (Temperature, surface workload, dehydration) that this value is just an approximation and can be used to compare dives, for example.

regards,
Matthias

[cparsons]

Ah - thank you, if the decompression is not based/dependant on this value then I am not so concerned, but I was puzzled by the statement

"the difference between your actual tissue load and the calculated load in the OSTC after some days may be different"

Is this because of rounding errors? Why would the calculated load be significantly different? I understand decompression is not an exact science, but are there accumulating inaccuracies?

I always stay well within the decompression envelope anyway, because I am an ancient 52 year old and like my beer too much but I am curious?

I normally have a 'morning off' with any period of repetitive diving, particularly if some of it is a bit deeper.

Thank you for the feedback

[heinrichsweikamp]

cparsons Wrote:
> Is this because of rounding errors? Why would the
> calculated load be significantly different? I
> understand decompression is not an exact science,
> but are there accumulating inaccuracies?

Hi,

no this is the honest information that the OSTC can only assume the actual load on a mathematical model. This model is well-known, used in thousands of computers from different manufacturers but it still is a model which gets less accurate for repetitive dives.
You'll find similar statements from all computer manufacturers.

regards,
Matthias

[cparsons]

Ah - I understand, you are saying the calculations are accurate according to the mathematical model, the same as any other dive computer?

I appreciate that a mathematical model is not representative of human physiology, I was more worried that the calculations were not accurate to this model itself?

I try to always give myself a large margin of safety, but even with that there are no guarantees unfortunately!

There are two of us on the trip with new OSTC's - be interesting to see how close the decompression times are to the Inspiration times, with the same Gradient Factors - we might even send you a postcard

Best wishes