Depth difference of 0.4m between two Perdixes

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hussler

New
Messages
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Location
Hondouras
# of dives
200 - 499
Hi there

I'm having a little quirk with my computer at the moment, I leant my Perdix AI to one of the tec instructors at my dive shop so he could run a course and all his students could have a Shearwater main and backup computer. He usually dives with a Teric and a Perdix and they always match, however, for this dive he gave Teric to the student and dove with his and my Perdix AI. But for the entire dive, my computer was showing 0.4m deep than his, so for example at the end of the dive my computer showed a CNS of 79% whereas his was 30ish%, amongst other things.

The only thing I thought of that could've effected this was the water type and I checked both are set to saltwater, is there any other setting that could be causing this or do you think the depth sensor might be off?
 
Is it possible to download both dives and compare them? That difference is large enough to suggest something else is going on besides depth differences.
 
go to your settings and check the pressure sea lecvel setting it should be 1013. that pressure I think defines I think what sea level is. It may only be valid for altitude but it also may be used for deco calculations. If that is so it is using it to determine ow much pressure is added to water presure to get bsolute. Just a guess. My thinking is that the tech guy looked at the barometer and saw it was other than 1013 and changed it to that days atmosphere pressure. Its a long shot I now because a 1/2 meter error would be about a 400 point on the 1013 setting. If worse comes to worse restore the computer to factory settings. otherwise You have a bad sensor.
 
There is no way that 40cm difference in depth can result in that kind of a difference in CNS loading. Something else must be going on here.

This.... No way. I dive with a Perdix AI and NERD 2. There is often 1 to 2 feet difference between the 2 Shearwaters (one is on my wrist, the other is on my face) There is never a substantial difference in NDLs, CNS or anything else...
 
Sorry guys, thanks for the quick replies, I completely forgot I posted this.

There is no way that 40cm difference in depth can result in that kind of a difference in CNS loading. Something else must be going on here.

I should mention that it was a deco dive, so breathing 50% O2 for roughly the 15 minutes from 19m to 6m and then a switch to 100% at 6m for 12 minutes.

Breathing 100% with a difference of 0.4m, I think could explain the CNS differences

go to your settings and check the pressure sea lecvel setting it should be 1013. that pressure I think defines I think what sea level is. It may only be valid for altitude but it also may be used for deco calculations. If that is so it is using it to determine ow much pressure is added to water presure to get bsolute. Just a guess. My thinking is that the tech guy looked at the barometer and saw it was other than 1013 and changed it to that days atmosphere pressure. Its a long shot I now because a 1/2 meter error would be about a 400 point on the 1013 setting. If worse comes to worse restore the computer to factory settings. otherwise You have a bad sensor.

Interesting, mine is showing surface pressure of 1039, this looks like it could be the problem. Is there a way to calibrate this without a factory reset?

The instructor may have forgotten to switch gasses on both computers at the same time.

Definitely switched at the right time.
 
Is it possible to download both dives and compare them? That difference is large enough to suggest something else is going on besides depth differences.
this is where id start- check not only the gas switching but make sure the correct gas was turned on in the first place - the dive profile will show any spike in po2 to get a high cns
 
Salt Water vs EN13319? Might Explain the depth, not the CNS though.
 

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