Adjustment for Pre-dive altitude change

[CaptainHornblower]

I live in Reno, NV, altitude 4500 feet and dive in Lake Tahoe, altitude 6200 feet. I use a Petrel and an Oceanic PP2. Both computers automatically adjust for altitude diving as long as you turn them on before diving so they can measure atmospheric pressure before the dive begins.

But neither, I don't think, can be programmed to take into account the 2K elevation change before the dive starts. If one were using tables you would start your first dive as a B repeditive diver.

My question: has anyone figured out a way of making the adjustment? I thought I might change the conservatism setting on the Petrel but haven't had time to play with it to see if adjusting the conservatism will approximate the necessary adjustments to the dive profile. My plan is to run some dive plans on the Petrel while at altitude with different conservatism settings and then run the calculations with Vplanner and GAP, with the pre-dive altidute change programmed in and then compare the profiles to see how they match up.

Thoughts?

 

[tbone1004]

your petrel is constantly tracking your tissue loading, even when in standby.

 

[CaptainHornblower]

So you're saying turn it on before I leave Reno in the morning and it might take the elevation change into account? I asked the tech people at Petrel and they didn't suggest that, but I'll try it and see what happens.

 

[tbone1004]

so the Petrel obviously doesn't track your altitude in real time, otherwise you wouldn't have to turn it on prior to descent at altitude.

Reno is at 4500ft, .82ata
Lake Tahoe is at 6500ft, .75ata

So here's what I'd do. Turn it on before you leave Reno, this gives it a baseline.
Turn it back on when you reach altitude. If you scroll to the tissue graph, you should see it move off of the base, though it likely isn't by much since it is less than .1ata/9% over the course of an hour....
Dive
It will likely keep tracking your tissues assuming at altitude if it shuts off while you're up there, so when you get back to the bottom, I'd turn it back on so it knows it's back at Renos altitude for the rest of its calculations.

 

[CaptainHornblower]

I'll give it a try and post what the results are.