Desat diagram

[ujacek]

On last Friday after dive I had this desaturation diagram. Numeric value (lead tissue saturation percentage) was 80%, but some lines/tissues was longer - up to (about) 100%. As I understand - lead tissue is a most saturated tissue and numeric value should have been 100.

[Solodiver]

The percentage value is just shown for N2, maybe your tissues has been saturated with He but desaturated from N2 completely (which is normal behaviour I see on my unit after every dive). Call it a bug or a feature, your choice.

Question: Why not display the value for He as well? Maybe on the right side...

HTH,
Jan

[ujacek]

> The percentage value is just shown for N2, maybe
> your tissues has been saturated with He but
> desaturated from N2 completely

It's true - but only if mix 28|0 means 28% He and 0% 02

> Call it a bug or a feature, your choice.

Feature? Like this?...

[dmainou]

To the best of my understanding your normal saturation (at sea level) is 80% (.79 bar) Nitrogen and 0% Helium.

Tissues get saturated with a time/doze (depth) relationship and may well go beyond 100% (1 bar)


So you are desaturated when your He gets to zero and your N2 gets to 80%

D

[PeterK]

Well I guess it is the percentage were the confusion comes from. Frankly speaking I had the idea that this is the percent value of the maximum tolered value before real decompression is required (M-value).

Maybe Matthias can bring some light into the darkness?

[dmainou]

page 18 of the manual...

D

[heinrichsweikamp]

This value is there due to historical reasons. If somebody has a better suggestion we can change it to a more meaningful information.

Or remove it and just show the leading tissue #?

Regards,
Matthias

[Solodiver]

Matthias, what exactly is the meaning of the current value? In my understanding the current behaviour with displaying 80% when in fact there are N2 saturated tissues is wrong, is'nt it? Would be interessting to know before one can make suggestions what to change.

What about showing the GF instead? This has been an often requested feature in here and would be a real benefit (IMHO)!

Thx,
Jan

[heinrichsweikamp]

Just look at the code

Displayed is "char_O_tissue_N2_saturation" of the leading tissue.

// N2 saturation in multiples of halftime for display purposes
// 0 = 1/8, 120 = 0, 249 = 8

80% is a fully desaturated leading tissue (Output shifted asymmetrically, you normally saturate your tissues much more then desaturating below the normal level at 1013mbar).

The GF is only computed in decompression situations.

regards,
Matthias

[Solodiver]

I still vote for showing the GF

Would'nt it be possible to calculate it (roughly( while calculating the desaturation, isn't this related? Obvisouly you know the saturation of the single tissues (at least you show a diagram and the saturation percentage), so GF should be known?

And if this is a motivation for you: The Preadator is showing the GF after the dive

Thx a lot,
Jan

[PeterK]

I agree with Jan. According to my understanding one can calculate the CF anytime, not only in decompression. After all, it is just the ration between current tissue pressure and M-value corrected by the ambient pressure.

[dmainou]

Jan, calculating the GF will require a lot of computing power.

The saturation graph makes a lot of sense for multiday diving.

You'll have a perfect graphical explanation of why you should rest after two our three days of diving 3 or 4 times a day as your middle compartments just won't go down fast enough.

D

[Gucky]

Hallo,

in einem anderen Beitrag hatte ich diesen Fall auch angesprochen.
Auch mir war die Anzeige der Prozentzahlen verwirrend.
Vorschlag:
Vor dem (ersten) Tauchgang ist die Sättigung prinzipiell 0%.
Die maximale Sättigung beträgt 100% und wird je nach Einstellung bei Erreichen des M-Wertes oder der GF-Linie angezeigt.
Eine Übersättigung sollte natürlich auch berechnet und angezeigt werden.
Die Grafik könnte bei 0 beginnen alle 6 Halbwertzeiten darstellen und so sehr anschaulich sein.

Dabei werden He und N2 gleich behandelt und es ist für alle leicht nachzuvollziehen.

by google ...
in another post I had mentioned this case as well.
I was also displaying the confusing percentages.
proposal:
Before the (first) is the saturation dive set 0%.
The maximum saturation is 100% and will be displayed depending on the setting when reaching the M-value or GF-line.
A supersaturation of course should also be calculated and displayed.
The graph could represent start at 0 every 6 half-lives and so be very descriptive.

It is He, and N2 are treated equally and it is easy to understand for everyone.

[dmainou]

Sorry, It doesn't work like that.

The 100% saturation can only work at a certain depth. Once a diver surfaces then the tissue gets supersaturated (>100%) vs the ambient pressure (100%). The m value is the maximum diferential in pressures between the ambient pressure and the tissue. Each compartment has its own M value.

I honestly think you guys are over complicating it.

N2 gets desaturated when it gets back to 80% and He gets desaturated once it gets back to 0%. It is a very clear representation of how much off gassing you still have to do.

I find it more useful when doing several days of diving with several dives each day as it clearly shows that those mid level compartments just don't get desaturated. This is why you should rest every third day or so.

That graph is a very clear representation of the decompression model in action.

D

[tiefunten]

Does the OSTC show compartment 1 at the top and compartment 16 at the bottom? I haven't got my unit here and am not sure about that.

[PeterK]

Well I disagree. Percent in my opinion is not a good way of displaying information as it always refers to some of basis. If that is unknown or unclear than the displayed number is of little value.
In case of the current fw on the surface it shows each tissue with 80% N2 (and 0% He).
The 80% is shown because the tissue is completely saturated with air (80% N2, 20% O2). Do I understand correctly?
If yes, I'm still unhappy. In my mind the tissue has a pressure of 0.8 bar N2, which is a much more meaningful number to me. During the dive the tissue pressure for N2 will rise and so will He, if present in the gas mix.
However, as long as I breath air, each tissue will show 80% N2 and 20% O2 all the time during the dive.

Maybe Matthias can explain a little more about this number.

[dmainou]

Maybe relable to .8 Bar?

[PeterK]

Displaying the tissue pressure in any unit is only meaningful if I know the maximum acceptable pressure (M-value). Therefore, I suggest to display in % of M-value.

However, I've been told that computing GFs takes a lot of CPU resources. If this holds true a similar resource consumption is associated with my suggestion. So might not be feasible with the currently used CPU.

[dmainou]

Hi Pete,

I would think that CPU is not a problem as the pc already calculated this during a dive but battery. On a day to day dive it wouldn't matter but on a liveaboard with multiple dives per day... you want your battery to last the whole trip without dying in the middle of the night.

It is likely that a usb charger is around but ot guaranteed.

On the M-value side M value is not the maximum value you can get but the "suggested" maximum pressure diferential between the saturation and the ambient pressure before syntomatic DCS appears on (I think) 0.05 of the cases (for some depths and 0.02 fo others)

I find a good indication to know that the mid to slow tissues are quite saturated after a couple of days. Regardless of the m-value I know I probably should rest as they ain't coming down fast.

I presume the same can be observed with a proposed M-value graph... Is there anything to be won if it gtes changed. Don't know, a dive phisician may give us a betteri insight.

D

[PeterK]

I agree, the number is for information only and does not add any significant value. Therefore, it does not make sense to sacrifies significant resources for computing this number. However, I believe the algorithm is continously computing current tissue pressure and comparing that with M-value. And that is done for each of the 16 theoretical tissues. If that is true then it is just a matter of displaying this information and this should not consume any additonal resources.

I'm aware about the meaning of M-value, maybe my post was just a little short. For me it would be good to know how far away the current tissue pressure of my leading tissue really is from the maxium level where no decompression stop is required. In my mind the number is eventually increasing througout the dive. Once the leading tissue is above its M-value (or the GF if used) I have to do decompression stops. During the stops the tissue pressure is slowly reduced until the M-value or GF for the next depth or the surface is reached. Am I wrong?

[Gucky]

Hallo,

hier mein Vorgehen zur Nutzung der Anzeige.
Da wie gesagt der Zahlenwert nur begrenzte Aussagekraft hat, habe ich das Diagramm abgeschalten. So erscheint es nicht immer im Tauchmodus.
Wenn es mich nach einigen Tauchgängen interessiert wie die Sättigung grafisch aussieht, schalte ich das Diagramm kurz ein.
Für einen solchen Überblick ist es ganz gut geeignet.
Ernsthaft benötige ich das Diagramm nicht. Glaube es geht den meisten so ...

by google ...
Here's my approach to the use of the display.
Because as I said has the numerical value of limited value, I've switched off the chart. So it does not always appear in dive mode.
If it interests me after a few dives grafically looks like the saturation, I switch the chart shortly.
For such an overview it is very well suited.
Seriously, I do not need the chart. Think it's the most so ...

[dmainou]

Yep, that's true.

I only pay attention to the graph after a dive and mor often than not only after a series of dives.

D

[James]

Hello,

Could someone please explain at what point on the desat diagram does a tissue become fully saturated so that decompression is required, to me this is not clear.

I previously had a Delta P Vr2 which had a similar desat diagram with a clear line indicating the point at which a tissue becomes saturated and decompression is required, I found this reference very useful, and would like to identify a similar position on the OSTC desat diagram. Maybe a solid line could included on the OSTC desat digarm to highlight this point.

Can anyone offer an explanation?

Cheers
James

[Solodiver]

To the best of my current knowledge this point is different for each tissue, so there had to be several markers.

It _might_ be, that the display on the OSTC is scaled and just going to the max. allowed value for each tissue, meaning if the bar for one tissue is reaching to the very end of the right side it might be fully saturated - but this is just a guess. If not, I'd suggest to think about such a feature .

Personaly I like to watch the tissue saturation while hanging an deco, nice feature!

HTH,
Jan

[James]

I agree the tissue saturation graph is a nice feature, and would be more useful if it was indicated where saturation occurs. From comparisons with my VR2 saturation of the lead tissue seems to occur at around 166%.

Cheers
James