Discrepancy between my computers during the dive

[pisauron]

Hello,

Been diving in Cyprus this week doing some cool wrecks.

Today i noticed something disturbing: My computers are showing me different NDL times.

1. Garmin descent mk2i with Buhlman 16c GF 70/85
2. Ratio ix3m 2 with buhlman 16c GF 70/85

The computers are on the same hand. This was in the second dive during the days. They were used simultaneously all the dives. They should show similar times.

So the Garmin shows significant more NDL (55 min) and the Ratio shows less (48 min). And this is after 3 minutes into the dive.

After ~half an hour the Ratio showed me deco times (NDL ended). The Garmin still had 15min NDL.

Anyone experienced this?

Which one makes more sense?

 

[nadwidny]

Has this happened before or is this a new issue?

 

[BRT]

I wear two identical Oceanic computers set for the same mix. Over 2 dives they get quite far apart because the depth sensors do not read exactly the same. They may be off by a foot or more, depending on the depth, and over 2 plus hours of multilevel diving that creates different NDL's. I could use either one and be confident that I knew what my NDL is. Wearing two different computers and expecting identical results will create frustration.

 

[scubadada]

Hi @pisauron

I assume both computers were set for the correct mix. That is a very large discrepancy.

If the profile was pretty square, you could check it on a a planner to see which was correct. Downloading the dive from both computers might help you.

I don't dive either a Garmin or a Ratio. Perhaps unlikely, but maybe a pressure sensor malfunction. Run the on board NDL planner on both to make sure they give correct NDLs. I have had a couple of very old Oceanic Pro Plus 2s fail when the pressure sensor was operating as if at higher altitude. This gave shorter NDLs.

 

[pisauron]

Has this happened before or is this a new issue?

I think it did but the difference was minor since i dived very shallow and didn't notice this.
Today dives were deep and the difference was notable

 

[pisauron]

Hi @pisauron

I assume both computers were set for the correct mix. That is a very large discrepancy.

If the profile was pretty square, you could check it on a a planner to see which was correct. Downloading the dive from both computers might help you.

I don't dive either a Garmin or a Ratio. Perhaps unlikely, but maybe a pressure sensor malfunction. Run the on board NDL planner on both to make sure they give correct NDLs. I have had a couple of very old Oceanic Pro Plus 2s fail when the pressure sensor was operating as if at higher altitude. This gave shorter NDLs.

Yes both are the same mix. Forgot to mention that.

I followed your advice and tried both planners on the computers.
I asked for 30m on 21%.
They show the same result of 12min. (Probably they are taking into account my surface interval on both).

 

[scubadada]

The planner results look OK, I would run them shallower, 20 m, with 32% to make sure they remain the same with a much longer NDL.

Sorry, I'm out of other ideas. Perhaps you just have to dive them again to see if it recurs. Maybe Garmin or Ratio would have ideas, particularly if you know which one is wrong.

Good luck

 

[pisauron]

The planner results look OK, I would run them shallower, 20 m, with 32% to make sure they remain the same with a much longer NDL.

Sorry, I'm out of other ideas. Perhaps you just have to dive them again to see if it recurs. Maybe Garmin or Ratio would have ideas, particularly if you know which one is wrong.

Good luck

Well no one of the other divers got deco and we all dived the same dives. So i think the Ratio is wrong.

I suspect the difference might occur from the "end dive" time of the Ratio. The dive ends automatically after 10min at surface.
While the Garmin ends immediately after hitting the surface. maybe over days that accumulated into major difference in NDL

 

[scubadada]

Well no one of the other divers got deco and we all dived the same dives. So i think the Ratio is wrong.

I suspect the difference might occur from the "end dive" time of the Ratio. The dive ends automatically after 10min at surface.
While the Garmin ends immediately after hitting the surface. maybe over days that accumulated into major difference in NDL

The end dive time will not affect the NDL. All the time is still at the surface for both computers. End dive time simply dictates how much time at the surface is needed before descending will be counted as a new dive vs. an extension of the previous dive.

 

[BoltSnap]

I suspect the difference might occur from the "end dive" time of the Ratio. The dive ends automatically after 10min at surface.

No, this has to do with the "minimum" surface interval to start counting any subsequent dive as a repetitive dive or a continuation of the prior dive. If less than 10 min, then the following dive is a continuation of the prior dive. If 10 min or more, then the following dive is a new "repetitive" dive.