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Hi,
I've got a question about desaturation times on the HW OSTC Sport.

We did multiple dives, after the last deep one (32m, 50 min, see profile in attachment), I had a desaturation of 34 hours. The next day I did another shallow dive (16m, 59 min).
After this dive my desaturation time was 9 hours.

If I calculate what my desaturation time would be just before the 2nd dive, it is 13 hours. (Time out dive 1: 14h30, time in dive 2: 12h30, so that's 21 hours surface interval, 34-21 = 13).

When I looked at my computer at the beginning of the 2nd dive, I saw that I was totally 'clean'. (I can't find these data in the profiles, but I remember the tissue bar being straight.)

I was wondering if this is normal, I was expecting another repetitive dive.

Secondly I would like to know why my desaturation time can decrease while diving.
(I saw the same decrease some weeks ago as well, also after first some deep dives and then a shallow dive, maybe it has something to do with the slow and fast tissues?)

Thank you in advance,
Lore

I just simulated your tissue graphs beginning of 2nd dive via ZH-L16A(table) /w spreadsheet.
[img]https://s9.postimg.org/mwz26mkn3/20160916_232808.png[/img]

Maybe tissue graph will be flat at the beginning of 2nd dive.
But I can't measure OSTC3's leading tissue selection mechanism and desat time calculations. sorry:(


Anyway while diving CNS==0, GF==flat weired, decompression calculation error will occurs mean depth shallower than tissue PN2????

Even with a flat graph you still may have some desat left. The resolution of the graph is not very big (50 steps or so).

Total desaturation would require infinite time so the OSTC assumes 5% saturation left for the desat time calculation. Desat time is re-calculated based on the actual ambient pressure after each dive (During the surface period it's a simple timer).

The actual tissue saturation is tracked with the ambient pressure every minute even in sleepmode and even slight changes of 20mbar (Weather changes) have some influence on this value.

One last word to Nofly times: As there are so many unknown variables (e.g. the actual cabin pressure in your flight) I follow a simple rule: 24h after each dive -> no flight.

regards,
Matthias

Matthias,
What you say is obviously correct, but still I'm left with the following question:

After the first dive that ended on 08/09 with a desat time of 34 hours and 19 mins, the diver would be desaturated on 10/09, 02:32.

The diver then does a second dive on 09/09, ending at 14:35, and is left with a desat of 9 hours and 20 minutes, and hence will be desaturated on 09/09, 23:55 (or a couple of hours earlier than after the first dive).

So by doing a second dive of 59 mins (although relatively shallow), the diver reduced her total desat time by over 2 hours.
Can that be explained?

Thank you in advance for your assistance.

Hi all,

even if the last post is quite old now, just to close this thread:
If the surface pressure has changed between the two dives, the desaturation time will be recomputed according to the new pressure. If the surface pressure reduces, your tissues will offgas faster. So to say, bad wheater (low air pressure) may not be good for one's mood, but it helps the diver to get the tissues down.
In firmwares somewhere post Version 2.26 the surface air pressure will be constantly monitored by the desaturation algorithm, so any changes in air pressure will constantly slave the desat time.

best regards,
Ralph