Discrepancy between my computers during the dive

[pisauron]

So i think i figured it out but i am not an expert and not sure.

Today i observed the two computers closely during the dives and noticed the Garmin updates info much faster the the Ratio.
I stopped moving completely and waited a few second and the Ratio catched up to the garmin and after a few seconds showed the same NDL.

So i think the discrepency happens because the garmin shows the info faster or perhaps it collects the data in faster HZ intervals.

Anyway, as promised here are the logs from both the computers for the dives tommorow. Again, i am not smart enough to read them in high level of understanding but they look the same to me pretty much.

Maybe someone else has a better idea.

Dive 1: Elpida
Dive 2: Zenobia

Thanks

 

[scubadada]

Hi @pisauron

I don't see how your observation today explains the large differences between NDLs you reported yesterday.

Can you read off the NDLs from your downloaded dives to compare them? Why do the graphs show 30/75?

 

[JMarc]

Why to the graphs show 30/75?

AFAIK, subsurface is displaying its own GF setting, not the one of the dive computer.

 

[pisauron]

I don't know why the graphs show 30/75 but both the computers are set to 70/85 as mentioned.

Today i also observed NDL discrepency but after a few seconds it was gone and the Ratio catched up to thr Garmin. Tommorow or Wednesday i will try to video film this live.

I don't think there is a way to show the NDL in the graphs.

 

[rhwestfall]

I don't think there is a way to show the NDL in the graphs.

only by dragging the mouse along the dive profile and reading the data from the floating menu for the point on the dive selected

 

[rhwestfall]

Yes, Subsurface has its own setting for GF, despite what the PDC is set to...

 

[Jai Bar]

I don't know why the graphs show 30/75 but both the computers are set to 70/85 as mentioned.

Today i also observed NDL discrepency but after a few seconds it was gone and the Ratio catched up to thr Garmin. Tommorow or Wednesday i will try to video film this live.

I don't think there is a way to show the NDL in the graphs.

The display might have a time-window average filter to show smoother changes. The calculations and logging can be done at different intervals.

For example, in Suunto computers, you can change the log sampling from 1 up to 30 seconds. This only affects the log so you can log more dives, but the NDL/Deco calculations are fixed at 1-second intervals and can't be changed.

 

[scubadada]

AFAIK, subsurface is displaying its own GF setting, not the one of the dive computer.

only by dragging the mouse along the dive profile and reading the data from the floating menu for the point on the dive selected

Yes, Subsurface has its own setting for GF, despite what the PDC is set to...

Thanks, I use Shearwater Cloud, works similarly to recover NDL and other dive data from the graph

@pisauron drag your cursor over your graphs and check the NDLs from the dives where you observed the discrepancies

 

[inquis]

drag your cursor over your graphs and check the NDLs

@pisauron, to be able to do this you have to first turn on the "Info Window" by clicking the "i" icon (top left of the graph). There may be two rows labeled "NDL:" shown:

• the one with "(calc)" at the end is based on Subsurface calculations and its gradient factors. (These are configurable, BTW.)
• The one without "(calc)" at the end is the dive computer-reported value.

 

[pisauron]

@pisauron, to be able to do this you have to first turn on the "Info Window" by clicking the "i" icon (top left of the graph). There may be two rows labeled "NDL:" shown:

• the one with "(calc)" at the end is based on Subsurface calculations and its gradient factors. (These are configurable, BTW.)
• The one without "(calc)" at the end is the dive computer-reported value.

Thanks I found it.

So yeah we have a problem.

I marked with a red star the spot i was checking on the graph.
After this point the Ratio stops calculating NDL since it's now a deco dive.

Notice how the Ratio shows: NDL 1 min.
Notice the Garmin: NDL 13 min.
Notice also the brighter green square at the top of the Ratio graph - I think it means deco ceiling. The Garmin doesn't have that.

So my guess about log sampling/info updates can't explain that.
Now i have no more ideas. But i tend to believe the Garmin more as it correspond to the other divers info as well.

Damn

On the bright side comparing the graphs from today's dives the discrepancy is only 1-2 minutes on both dives every point i check. I will continue with my plan to video the event in the next days.