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I checked the NDL calculation in Subsurface and could not find any code that uses an assumed ascent rate.

We've already discussed that a predetermined ascent rate is used for some data but it doesn't mean that the rate is used in the calculations for NDL and deco. You need to look at the actual calculations to prove it one way or the other.

There is nothing in the Important message box above (and in information from other versions of the Perdix manuals that I've looked at) that indicate that an "assumed" ascent rate applies to calculations for NDL. For what its worth Erik Baker does not use an assumed ascent rate in his...

You said: "Put another way my instantaneous ceiling could be 20m (#1), but my "actual" (bad name) ceiling could be 15m, because as I ascend from 80m I offgas and I would be able to continuously ascend at whatever my configured ascent rate until I got to 15m and had to stop." This is exactly...

I posted some replies earlier in this thread and elsewhere regarding how ceilings and NDL are calculated. You can search for those responses. After reading the recent posts (dated 2024) I realized that I might be misunderstanding what you and others say by "assuming". So, there are two...

The A, B, and C tables for nitrogen and the table for helium can be found in Baker's paper "Understanding M-values". I've included it here for your convenience.

On the Perdix SurfGF is displayed post dive and counts down to zero as the leading TC off gasses. It might be displayed as GF99. I don't remember exactly. Whatever is displayed, SurfGF is equal to GF99 on the surface. I don't know what data and how long it gets logged once on the surface since I...

Unless I'm misunderstanding you you seem to suggest something opposed to what Erik Baker PE said. In his paper "Understanding M-values" he said, "This included M-values which expressed a linear relationship between ambient pressure and tolerated inert gas pressure in the hypothetical tissue...

I watched the video on hand signals. One handed signals is what I use and I've had mixed success in teaching my buddies to adapt them. Alas, old habits die hard. Cave divers use one-handed signals because frequently the other hand is occupied. The instructor in the video is using a variation of...

I misunderstood your original post. The two tanks are in parallel so given the same SAC rate you had more gas left than they did even though your tank pressure was less than yours. I still stand by what I said earlier, i.e. don't lie about remaining pressure. I agree with what others said that...

I meant to say the OP's gas consumption resulted in using 4000 psi of gas on the first dive versus 3000 psi for the other divers.

First, NEVER lie about gas remaining. Let's say it's a group dive and the DM gets everyone's tank pressure. He decides everyone has enough gas to swim farther from the ascent point. But, you lied and you eventually signal low on gas. The DM can't take the rest of the group back to the ascent...

Let's compare two profiles with these GF's: 65/80 to 95/80. Dive parameters: air to 180 ft for 20 min, 60 ft/min descent rate, 30 ft/min ascent rate, no deco gasses. 65/80: deco = 58 min, surfGF = 77, 1st stop = 60 ft, CTC at 10 ft = 7 with HT of 54.3 min. 95/80: deco = 52 min, surfGF = 78, 1st...

If you are not surfacing with a GF greater than 80, why not just set GFHi to 80? Then the computer will adjust the NDL or deco depths and times to bring you to the surface at or below 80.

In my above post I chose two dives with GFLo/GFHi of 30/80 and 80/30 because the graph I included used those GF's. Using the same profile as above but changing the GF's to GFLo/GFHi = 70/90 and 90/70 gives these results for a profile using: air to 180 ft for 20 min, 60 ft/min descent rate, 30...

Some studies indicate that some deep stops were maybe too deep. So, the tendency now is to make the first deco stop shallower by setting GFLo higher. But, reversing GF's so that GFLo > GFHi is not the way to plan for shallower first stops. In fact depending on the GF's used could result in a...

Yeah. It's not how you look getting into the water, it's what you look like under the water that counts.

Fixed it. Clicking on the link above will work.

I forgot about TTS (time to surface). Of course, an assumed ascent rate is needed to calculate the time it takes to get to the surface without exceeding GFHi. I was thinking only of the calculations for ceiling and NDL NDL doesn't need to predict the ascent rate because it is concerned solely...

That's correct. At the current time, there are no dive computer options you can download that mimic crystal balls.