Discrepancy between my computers during the dive

[dmaziuk]

Indeed the Ratio computer is greatly more conservative then the Garmin. But i trust the Garmin more.
Anyways the Ratio cleared the deco by itself since i ascend slowly anyways and the deco was 1-2 min max. Also my GF is 70/85 that pushed the first stop to 6meters anyways.

But moving forward with longer deco dives i suspect the Ratio will demand crazy deco times that i simply don't have enough gas for. Meaning i might skip some, and might cause a lockout. We'll see.

Any idea why they show different CNS tox?

And the wrong way around, too, as ratio's 26% would imply higher O2% and thus longer NDL.

 

[Germie]

This is nothing special. It is just about how the software developer implemented the algorithm and the surface intervals. There always can be differences.
I could have 55 minutes difference between Heinrich Weihkamp and Shearwater on the same cave dive, just because of how all things are implemented. I have taken pictures of this in the past.
Remember there is no strict absolute way when you get bent and when not.
If you ask or sb 10 software developers to write code for Buhlmann, you will find 10 different solutions. Even if everybody will write it in Java or so.

 

[JMarc]

Somewhat relevant : Why is Bühlmann not like Bühlmann ?

 

[pisauron]

Did you check if altitude settings on the Ratio is not set to an elevated altitude?
This would shorten ndl and prolong deco.

I think the Rtio takes elevation reading by itself.

 

[steinbil]

Somewhat relevant : Why is Bühlmann not like Bühlmann ?

I don't think the finer nuances of implementation can account for such a large discrepancy as shown in this thread. To quote the article you linked:

"So in summery, even if two implementations follow the letters of the definition of a decompression model, they might come up with different deco plans. For all practical purposes, those differences should be small (like a few percent of total decompression time)"

This is nothing special. It is just about how the software developer implemented the algorithm and the surface intervals. There always can be differences.
I could have 55 minutes difference between Heinrich Weihkamp and Shearwater on the same cave dive, just because of how all things are implemented. I have taken pictures of this in the past.

Really? 55 minutes difference in deco time/NDL on two implementations of the same algorithm and GF on a singular dive? Can you provide the details/profiles, please?

 

[pisauron]

Any idea why they show different CNS tox?

And the wrong way around, too, as ratio's 26% would imply higher O2% and thus longer NDL.

Maybe because the Ratio went into deco it shows higher CNS %?

 

[scubadada]

Maybe because the Ratio went into deco it shows higher CNS %?

Hi @pisauron

No, CNS% is time of exposure and ppO2. It doesn't matter if there was deco or not.

The discrepancy in CNS% is interesting in addition to the NDL difference. I would alert Ratio to both in your communication.

If your Ratio computer is operating at the wrong atmospheric pressure/altitude, it might explain both the shorter NDL and the higher oxygen exposure. Can you find the surface pressure for your dive on the Ratio as I am able to do for my Teric in the Shearwater Cloud?

 

[Germie]

I don't think the finer nuances of implementation can account for such a large discrepancy as shown in this thread. To quote the article you linked:

"So in summery, even if two implementations follow the letters of the definition of a decompression model, they might come up with different deco plans. For all practical purposes, those differences should be small (like a few percent of total decompression time)"


Really? 55 minutes difference in deco time/NDL on two implementations of the same algorithm and GF on a singular dive? Can you provide the details/profiles, please?

Not anymore as the Heinrich Weihkamp died.
But it was a cavedive. 360m at a maximum depth of 11m, then a 100m at 30m, then to 45m. The way back was again the long time at 10m, and the Shearwater counted back, the Heinrich weihkamp did not.

I have had the same thing in march on a dive to only 25m in Mexico. Suunto D5 (ok, fused Suunto RGBM), and Shearwater 40/75. At 12m the Shearwater counted back where the D5 said 'DECO'.

This means there is a difference between the programmers about the 'offgassing'. Computers with Buhlmann are easy to write code for, as long as you use the simple modell of getting down, stay at 1 depth, go up. You only have to implement a table which was given to every open water diver when they started their course 10 years and longer ago. Also this tables gave you decompression times. There was already some variables like DCIEM vs Padi/naui, but these tables are quite easy to implement in a computer.

As soon as you start doing things that are not that easy, the programmer has to write more difficult code. For example multi level. But also the shallow part first, then the deeper part, or jojo-profiles.

And the most difficult part is when a diver decides not to do a stop as expected. The right computers will recalculate the dive. The bad computers will show '505', SOS mode. So computers that go in '505' are always a nogo for me,but are cheaper to develop for the manufacturer.

Then if you have made the computer, it must be tested. And here it starts, you cannot do ALL testing, so you have to decide what are the risks (risk based testing). The group of divers that does cavedives is not that big, so the biggest differences between computers due to programming errors are probably seen here. For recreational dives, the differences are small. 3 minutes difference is small in my eyes. This can already happen if you implement a different NDL. Just look at tables, is the NDL for air at 30m 15 minutes (DCIEM) or 20 minutes (Padi/Naui)?

CNS calculations are quite easy to implement, just PO2 and pressure and time needed. If there are big differences between 2 brands, one of the brands has made a mistake in the calculation.

 

[Germie]

And I forgot, most times you will NOT see big differences between computers on the first dives. If you do multiple dives a day and days behind each other, the differences start to appear. This has to do as I said with the calculations of 'offgassing', residual nitrogen.

When I teach a cave course in France, you always see that the older Suunto's like the Viper (without the word novo) got 'deco under the shower' at the end of the week. Probably this has to do with some jojo-profiles you have to do due to the way the cave goes (Saint Georges, you go first to 29m, then after 400m you surface almost ,2-0m depth, sometimes we surface in the airbell, then you go back and you have to go over the 29m again. The newer Suuntos don't have this 'deco under the shower' behaviour. So they changed the algoritm for this. Again no Buhlmann, but with buhlmann it will be the same between brands.

 

[pisauron]

Not anymore as the Heinrich Weihkamp died.
But it was a cavedive. 360m at a maximum depth of 11m, then a 100m at 30m, then to 45m. The way back was again the long time at 10m, and the Shearwater counted back, the Heinrich weihkamp did not.

I have had the same thing in march on a dive to only 25m in Mexico. Suunto D5 (ok, fused Suunto RGBM), and Shearwater 40/75. At 12m the Shearwater counted back where the D5 said 'DECO'.

This means there is a difference between the programmers about the 'offgassing'. Computers with Buhlmann are easy to write code for, as long as you use the simple modell of getting down, stay at 1 depth, go up. You only have to implement a table which was given to every open water diver when they started their course 10 years and longer ago. Also this tables gave you decompression times. There was already some variables like DCIEM vs Padi/naui, but these tables are quite easy to implement in a computer.

As soon as you start doing things that are not that easy, the programmer has to write more difficult code. For example multi level. But also the shallow part first, then the deeper part, or jojo-profiles.

And the most difficult part is when a diver decides not to do a stop as expected. The right computers will recalculate the dive. The bad computers will show '505', SOS mode. So computers that go in '505' are always a nogo for me,but are cheaper to develop for the manufacturer.

Then if you have made the computer, it must be tested. And here it starts, you cannot do ALL testing, so you have to decide what are the risks (risk based testing). The group of divers that does cavedives is not that big, so the biggest differences between computers due to programming errors are probably seen here. For recreational dives, the differences are small. 3 minutes difference is small in my eyes. This can already happen if you implement a different NDL. Just look at tables, is the NDL for air at 30m 15 minutes (DCIEM) or 20 minutes (Padi/Naui)?

CNS calculations are quite easy to implement, just PO2 and pressure and time needed. If there are big differences between 2 brands, one of the brands has made a mistake in the calculation.

But the difference was not 3 minutes. It was 10+ minutes. Same algorithem, same dives, same everything. And simple dives as can be seen in the graphs.

It's not a minor difference and shouldn't be dismissed.