On a NDL dive, which computers' NDLs are not affected by GFLo?

[scubadada]

I think the table might need to be more like no / marginal / yes ... (reason in post #46) ... bit of chicken and egg as it depends on the results.
no - GFLo does not affect NDL on a NDL dive
marginal - GFLo does not typically affect NDL on a NDL dive and/or the effect is very minimal
yes - GF Lo affects NDL on a NDL Dive...

I don't understand the "marginal" response. Do you have any examples of this? The GF low either changes the NDL or it doesn't. We know that the GF low does not affect the NDL for Shearwater or Dive Rite. We need others to check the other brands. I would think the answers will be no or yes. Though I recall your exchange with Ross regarding Technical Dive Computers, I would still like to see someone run the planner to confirm.

 

[dmaziuk]

You left out the fact that the algorithm and Baker's mods to it apply to calculating a dive plan - not maintaining a real-time calculation on the fly.

Deliberately, yes. But that's the argument: what a computer does on a no-stop dive can't be what Baker invented.

I don't see how anyone can say that is wrong to do it the way Shearwater does it - which doesn't utilize GF Lo until such time as it detects that GF Hi would be exceeded on a continuous ascent (at 30ft/10m per minute).

Two problems:

• the simple one is that the user interface is lying to you: on a no-stop dive you are not diving 50/80 (or whatever). You are diving 80/80.
• The worse one is that when you've just exceed your NDL, you have a stop just under the surface. At 3 metres, to be exact. Now you are diving 50/80 and your gas loading at the surface is 80.00001% of the base M-value. However you have to be at your 3-metre at stop with 50% of that M.

I don't see how you can make a roll-over from no-stop to deco smooth without fudging the code to do something that was never part of anything Buhlmann or Baker ever created.

Think of the numbers if it makes it easier. Take Haldane's 2:1 as the base M-value. Surface pressure is 1 bar. At GF Hi 80 you need to surface with 80% of 2*1 bar in your leading tissue: 1.6 bar. 3 m stop pressure is 1.3 bar. At GF Lo 40 you need to be at 3 metres with 40% of 2.6 bar in your leading tissue: 1.04 bar. Do you think that is actually doable if your surfacing loading is at 1.6 bar already?

 

[stuartv]

Deliberately, yes. But that's the argument: what a computer does on a no-stop dive can't be what Baker invented.

My last post in this thread on this particular subject.

As far as I know, Baker invented TWO things: An algorithm (based on Buhlmann ZHL-16B/C), AND an implementation of that algorithm to suit a specific purpose.

A dive computer absolutely CAN have its own implementation of the algorithm that he invented, though it be for a slightly different purpose.

An implementation that meets the requirements of the algorithm (uses a GF Hi and Lo to implement a sloped approach to surfacing with some percentage of the M-value) CAN be "what Baker invented". 2 different implementations CAN produce somewhat different results and still both be valid implementations of the algorithm (that Baker invented).

If you are still not clear, let me refer you the last paragraph in this old post from @RonR:

New dive computer for Divemaster internship

 

[dmaziuk]

The GF low either changes the NDL or it doesn't.

Not quite: for a given GF Hi, there should be a GF Lo cut-off at which it does not change the NDL regardless of the implementation. GF Lo lower than that cutoff would change the NDL if implemented that way.

 

[tursiops]

GF Lo lower than that cutoff would change the NDL if implemented that way.

You may be catching up! This thread is about which computers have such an implementation, if any.

 

[dmaziuk]

You may be catching up! This thread is about which computers have such an implementation, if any.

You still don't get it: I can "implement it" by not letting the user chose arbitrary GFs. I give them the choice of pre-set GF pairs that don't cause this problem, and the question becomes moot: I can have that implementation and it will make no difference to the NDL.

 

[scubadada]

The GF high is the absolute determinate of the NDL. This includes a normal ascent from depth.

 

[dmaziuk]

The GF high is the absolute determinate of the NDL. This includes a normal ascent from depth.

In that case the answer to OP's question is "all of them".

 

[Jay]

I don't understand the "marginal" response. Do you have any examples of this? The GF low either changes the NDL or it doesn't. We know that the GF low does not affect the NDL for Shearwater or Dive Rite. We need others to check the other brands. I would think the answers will be no or yes. Though I recall your exchange with Ross regarding Technical Dive Computers, I would still like to see someone run the planner to confirm.

The 'marginal' bracket was driven by a few things; SubSurface info above and his blog post (Ross also responded in that post), MultiDeco info earlier in the thread (caveat: I think @rsingler was going to verify that post vacation) and Ross' response which initially (partially said) said "GF requires different settings when used on intentional NDL / almost deco dives. The GF Lo setting has to be shifted towards the Hi, or else that GF Lo will trigger unwanted stops.". If/assuming MultiDeco(and TDC-3) stops may/mayn't be all be all cleared, but might be very minimal, hence the minimal NDL affect (to those stops). I am not certain about this and would prefer to let the MultiDeco discussion continue by those more familiar with it (unless the TDC-3 does have the ability to Custom GF ...).

 

[dmaziuk]

Ross' response which initially (partially said) said "GF requires different settings when used on intentional NDL / almost deco dives. The GF Lo setting has to be shifted towards the Hi, or else that GF Lo will trigger unwanted stops."

Yep. Think about it: your "deco slope" is from the mandatory 3 m stop to the surface, the whooping 0.3 bar. There isn't much room for "gradients" there. The only question is how you program around it so that you can keep your GF-Hi NDL and have your GF Lo on planned deco dives too.