The math guys tell us that Buhlmann GF wasn't designed to give us meaningful numbers with changing surface pressure.
And the Schreiner equation doesn't allow it at all, apparently.
But thinking simplistically, if exceeding a tissue pressure ratio of 2:1 is a bad thing (GF>100), and you reduce the denominator by driving to altitude, you should be able to quantify the change, if you know current pressure at altitude, and calculated leading compartment partial pressure from the previous dive.
I'm talking with one of our folks to see if there's a way to at least look at some numbers. Yes, driving to 2000' may be only like ascending another 2' in water (and I'm not picking on you,
@broncobowsher), but when comparing all your tissue loading with a "surface" that is now ~5% lower in pressure means you're
maybe looking at a >5% bump in gradient (not accounting for offgassing during the drive). After many repetitive dives and full slow tissues, you may be happy with surfacing at GF75, but maybe
not happy with that rising to 80 during your drive. It would be nice to examine this concept in detail, with guys that understand gradients.
I think everyone can buy into not popping to 7,500' cabin altitude, and instead using some blanket wait time to account for those divers with full slow tissues. But the drive to altitude problem is one that us Tahoe divers confront regularly. You're already gas stressed by surfacing at 6,000'. You were conservative and are happy with your status. But it's Sunday afternoon, and you have to crest 8,000' very briefly on the drive home.
Realistically, how long should you wait? Why can't we use a mathematicsal model to help us understand this, based on all the data we've acquired in a very similar situation (diving)?
Thank you to
@Shearwater for telling us how our toy calculates part of its data!