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Correct if it's seawater, specifically with a density of 1.020 g/mL, which is the value assumed by EN13319.

Starting with 1 atm = 14.6959 psi or lb/in^2, this equates to 10.354 meters fresh water (from 14.6959 * 1000 / 2.2 / 2.54^2 / 100). Divide by 1.024 (average saltwater density) for 10.11 msw. Divide by .3048 for ft of either.

Shearwater's GTR is against a user-configurable reserve. It's a simple matter to make this the Rock Bottom amount for the planned depth. (I quite agree that knowing how to calculate RB on the fly is important for multi-level dives: e.g., 10D+300 psi for an AL80 with depth in ft will handle a 2...

Take an honest look at your trim in the water. If you look like a seahorse, fix that before going into the cenotes. I second CenoteXperience.

Ballpark 3700-3750 psi. That allows for a 100-110°F tank cooling to 3500 at 70°F. The two big contributors are how fast is the fill and how empty it was to start.

I was never able to do that in a jacket either. It always slipped up (jacket shoulders around my ears, my armpits against the pockets) no matter how tight the waist strap/cummerbund was fastened. (This was with a weight belt, rather than integrated weights.)

For your DM work where you will remove the rig at depth (this simulates an entanglement issue when you've lost your buddy, BTW), I suggest putting some weight on a weight belt on your person. This reduces the likelihood you will lose your grip on the rig and rocket to the surface.

Shoulder straps are too tight. If you lose wing and suit inflation and you're unable to stay on the surface, just ditch the rig (or give it to your buddy, or clip it to the DSMB you or your buddy may have deployed earlier).

Have you tried a new battery in the problem transmitter?

One of the more illustrative vids on the harness:

I believe I've read similar accounts (perhaps on CCRExplorers?) where an increase in their GFLow was said to be beneficial. I'm certainly not in your shoes, but some of the deco researchers are doing similar depths but no longer at 20/70 or 30/70. Depending on how you're padding the various...

No, you're misunderstanding. You are both swimming in the same direction: them in front swimming away, and you behind swimming toward them. There is a consistent 10m separation because you're both swimming at the same pace. When a problem develops, you have to catch them. You increase your...

I think I should elaborate: if you're 10m apart, swimming 10m/min and they're swimming 8m/min away from you -- as is the case if they're leading -- how long until you can grab their fin? For most, I think the answer is, "too long".

Yes, there are problems here. One of the biggest is they won't necessarily be stationary.

Brass zips get waxed. Plastic zips get silicone grease (or similar, like Ti-Zip) at the closed end.

I don't disagree. Another simple solution is to have a personal limit of X min remaining NDL. Yes, this also results in a variable margin, though it does increase as one goes deeper (for the same value of X). I don't have a solid answer for the general populace. Personally, I'm willing to update...

Not knowing how much conservatism is needed plagues the "pretend it's air" approach as well. Perhaps on 36% they're unlikely to have an issue, but on 28% they might. The risk clearly increases, which was the main point I was trying to make.

These approaches seem equally clear: 1. Pretend you're diving air when you're not -- definitely results in a gas-dependent / variable safety margin. This also deactivates any MOD warnings, but surely they won't lose track of their depth, right? 2. Use the computer's safety features as designed...

For gas blending, I think temperature consideration is critical. I use VdW and adjust the target pressure for measured temperature (estimated with an IR temp gun). I routinely hit within 0.1 of my target mix on the helium fraction. (That fraction is extremely sensitive to the final top-off...

Hardly a recommendation, but if I had reason to suspect that I had a PFO, I would back off to something very conservative, perhaps GF x/60. Times would be about half that of someone with "Medium" conservatism of x/85. If that allowed me to do the dives I wanted, cool. If I wanted to stay longer...