Discrepancy between my computers during the dive

[harvalen]

If you look at the logs you will see the CNS changes. Dives start with CNS lower than the previous dive-end CNS.

If you look closer. For example the two dives on the 28th. In the Ratio logs the first dive starts with CNS 6% and ends with CNS 17%, the second dive starts with CNS 16% and ends with 29%. In the Garmin logs the first dive starts clean with CNS 0% and ends with CNS 11%, the second dive then starts at CNS 5% and ends with CNS 20%. So at least form a CNS perspective they are treating the surface interval very different, while the increase during the dive is pretty close.

 

[pisauron]

If you look closer. For example the two dives on the 28th. In the Ratio logs the first dive starts with CNS 6% and ends with CNS 17%, the second dive starts with CNS 16% and ends with 29%. In the Garmin logs the first dive starts clean with CNS 0% and ends with CNS 11%, the second dive then starts at CNS 5% and ends with CNS 20%. So at least form a CNS perspective they are treating the surface interval very different, while the increase during the dive is pretty close.

Indeed. Ratio response was:

In addition to the above, in this specific case, we can see that the two computers start the repetitive dives with different CNS values. The CNS value does not influence the decompression calculation (at least it does not on the RATIO, but I believe Garmin does not consider it either), but it might indicate that the two computers off-gas the tissues slightly differently.

 

[harvalen]

In addition to the above, in this specific case, we can see that the two computers start the repetitive dives with different CNS values. The CNS value does not influence the decompression calculation (at least it does not on the RATIO, but I believe Garmin does not consider it either), but it might indicate that the two computers off-gas the tissues slightly differently.

If CNS is supposed to decrease in proportion to off-gasing of the tissues in the RATIO computer, and not some odd 24 hr reset, then it seems to be doing very little off-gasing during that 93 min surface interval. I wonder why Ratio would comment on it, but not be interested enough to dig deeper into the difference.

 

[pisauron]

If CNS is supposed to decrease in proportion to off-gasing of the tissues in the RATIO computer, and not some odd 24 hr reset, then it seems to be doing very little off-gasing during that 93 min surface interval. I wonder why Ratio would comment on it, but not be interested enough to dig deeper into the difference.

Is it possible that the difference in CNS is caused by a "faulty" surface interval timer? This can also explain the NDL discrepancy.
For expamle dive1 ends, the Ratio counts 3 min (instead of an hour) then dive2 starts, CNS is barely changed, and NDL is affected greatly.

 

[harvalen]

Is it possible that the difference in CNS is caused by a "faulty" surface interval timer? This can also explain the NDL discrepancy.
For expamle dive1 ends, the Ratio counts 3 min (instead of an hour) then dive2 starts, CNS is barely changed, and NDL is affected greatly.

It would explain both issues. Simplest explanation I can think of is that someone didn't consider the computer going into deep sleep during the surface interval to save battery and those calculations now happens less often than they expected, resulting in less off-gasing and CNS not decreasing as much.

Another explanation would be that someone listened too much to arguments like in that other thread and added a penalty for short surface intervals.

 

[pisauron]

It would explain both issues. Simplest explanation I can think of is that someone didn't consider the computer going into deep sleep during the surface interval to save battery and those calculations now happens less often than they expected, resulting in less off-gasing and CNS not decreasing as much.

Another explanation would be that someone listened too much to arguments like in that other thread and added a penalty for short surface intervals.

Alright then i will send a question to Ratio.
Although i can't think of a way to confirm this is what happens from looking at the logs.

 

[scubadada]

Hi @pisauron

One easy thing to do would be to record start and end CNS O2 for all of the dives during that last series to compare the decreases during SIs, including overnight. I could not specifically find how Ratio handles O2 elimination in the user's manual. There are 2 general methods, the 90 min half-life and cliff vesting at the end of a 24-hour period. My Shearwater uses the former, my Oceanic the later. I assume Garmin and Ratio both use the 90 min half-life. Each day should start clean, 0%, given the long time overnight.

From @harvalen post:
Garmin 0-11% and then 5-20%
Ratio 6-17% and then 16-29%

Garmin starts clean, decreases about 1 half-life (90 min) between dive 1 and 2. Ratio starts at 6% and shows nearly no decrease between dive 1 and 2.

The differences in NDL are a different matter and beyond an easy calculation for me, perhaps someone else.

 

[pisauron]

Hi @pisauron

One easy thing to do would be to record start and end CNS O2 for all of the dives during that last series to compare the decreases during SIs, including overnight. I could not specifically find how Ratio handles O2 elimination in the user's manual. There are 2 general methods, the 90 min half-life and cliff vesting at the end of a 24-hour period. My Shearwater uses the former, my Oceanic the later. I assume Garmin and Ratio both use the 90 min half-life. Each day should start clean, 0%, given the long time overnight.

From @harvalen post:
Garmin 0-11% and then 5-20%
Ratio 6-17% and then 16-29%

Garmin starts clean, decreases about 1 half-life (90 min) between dive 1 and 2. Ratio starts at 6% and shows nearly no decrease between dive 1 and 2.

The differences in NDL are a different matter and beyond an easy calculation for me, perhaps someone else.

Thank.
Seeing as the Ratio starts a fresh day with 6% CNS isn't that strange since it has been 24h~ between the previous day dives?

 

[scubadada]

Thank.
Seeing as the Ratio starts a fresh day with 6% CNS isn't that strange since it has been 24h~ between the previous day dives?

Yes it is, why I mentioned it.

You could also pick an NDL near the lowest of each dive and compare the 2 computers at that same time point.

Between the CNS O2 and NDL data, you would have quite a bit to help ferret out the problem, share with Ratio.

 

[Jai Bar]

Yes it is, why I mentioned it.

You could also pick an NDL near the lowest of each dive and compare the 2 computers at that same time point.

Between the CNS O2 and NDL data, you would have quite a bit to help ferret out the problem, share with Ratio.

Since the manufacturer got these logs, I'd expect them to turn every stone and then some, in order to nail this problem and make sure there is no dangerous bug or some that they may have overlooked during testing. Their answer that says everything is alright is strange from my point of view. They could at least try to reproduce the problem, simulate something similar, try under extremer conditions etc. and only then at least say that hard as they have tried they did not find any problem. At this stage, I would have asked the diver to send his unit for further testing, providing him a replacement for the time being.

I sincerely hope that after rigorous investigation they find everything is okay or maybe only a faulty unit and that's all.