When is ZH-L16C GF not ZH-L16C GF? When it is a G2 Tek computer

[lexvil]

So one should plan their dives with the G2tek and then leave it behind and dive SW, HUD, Garmin and the extra gas will will be in the plan.

It’s bad enough the SP has ignored the latest standard but also their own GF in the hud.

 

[Sevenrider860]

Is it possible that your G2 Tek is set to assume a last stop depth of something other than 10'?

Alternatively, I wonder if the discrepancy is coming from the G2 Tek assuming slower ascent rates, per its Ideal Ascent Rate chart.

I checked that and I do not see any option to change the last stop depth and I know during my in-water testing the computer showed a 10 foot stop requirement.

The variable ascent rates could be a factor. The Scubapro HUD also uses variable ascent rates (see below), but they specifically state that they use a descent speed of 20m (66ft)/min and an ascent speed of 10m (33ft)/min in the Dive Planner. The Scubapro HUD is also dual algorithm, so I don't know if these apply to both algorithms. I don't really have a way to duplicate the published G2 Tek ascent rates to see if they are being used in the Dive Planner.

 

[scubadada]

Perhaps "should not" is more accurate. I can see a poor implementation screwing this up and appreciate the verification by @Sevenrider860.

Edit: need more coffee... so... slowww.

Ha, OK, for properly implemented Buhlmann... Do you or @Sevenrider860 have an example of a poor implementation where GF low affects the NDL?

 

[inquis]

iDeco Pro is one, based on this past discussion. FWIW, Shearwater no, MultiDeco no, Subsurface no, TechDeco no.

 

[stuartv]

Ha, OK, for properly implemented Buhlmann... Do you or @Sevenrider860 have an example of a poor implementation where GF low affects the NDL?

I'm pretty sure I remember posts on SB in the past where somebody verified that hanging GF Lo on their computer did change the NDL they were shown in the computer's planner.

But, I don't remember what computer it was.

EDIT: Or maybe it was planner software and not an actual dive computer. As shown in the post @inquis linked.

 

[Sevenrider860]

Ha, OK, for properly implemented Buhlmann... Do you or @Sevenrider860 have an example of a poor implementation where GF low affects the NDL?

I do not have actual experience or knowledge of one. But I believe there were some posts in 2019 specific to this subject were it was said it was possible that the TDC-3 could be affected based on some answers from Ross Hemingway about the GF Low needing to be shifted towards GF Hi on NDL dives.

 

[dmaziuk]

I've heard mentioned (though I don't know if that applies to the Scubapro G2 TEK) that some manufacturers will automatically increase the conservatism if a deco or safety stop is missed or has not been completed.

That would be a seriously dumb idea because the safety stop is by definition optional (except when using PADI tables) and missing the deco stop means you're bent as far as the algorithm is concerned. Increasing conservatism at this point only makes you "more bent" -- again, as far as the algorithm is concerned.

Decreasing conservatism after omitted deco stop would make some mathematical sense, but is otherwise questionable. Like, if I had an actual reason to set my GF High to 70, I will probably not appreciate my computer quietly changing it to 85 mid-dive.

 

[Sevenrider860]

That would be a seriously dumb idea because the safety stop is by definition optional (except when using PADI tables) and missing the deco stop means you're bent as far as the algorithm is concerned. Increasing conservatism at this point only makes you "more bent" -- again, as far as the algorithm is concerned.

Decreasing conservatism after omitted deco stop would make some mathematical sense, but is otherwise questionable. Like, if I had an actual reason to set my GF High to 70, I will probably not appreciate my computer quietly changing it to 85 mid-dive.

If you set your GF at 70 and miss a deco stop, you already said “missing the deco stop means you're bent as far as the algorithm is concerned”. So the computer adjusting GF to 85…not mid-dive, but after your missed GF 70 deco stop means you are not bent as far as the algorithm is concerned. It does not hide this change…it is clearly displayed. You can then intentionally pad some shallower stops while keeping the algorithm in the “not bent” side of the GF 85 line. There is no Surface Gradient value like Shearwater and Garmin provide.

Honestly, I am not too bothered by that behavior. I have only seen it kick in during pressure pot testing, not on actual dives.

What is interesting is that the HUD manual does not describe the adjustment of GF if you miss a deco stop. It does auto adjust MB levels if your are using the proprietary algorithm, but does not say anything about adjusting GF if you are in the ZH-L16C+GF mode.

 

[dmaziuk]

Honestly, I am not too bothered by that behavior. I have only seen it kick in during pressure pot testing, not on actual dives.

That only means you're setting your GF High to 70 for no reason whatsoever, you could have set it to 85 from the start if you're OK with it happening mid-dive... and that is the "confusion of ideas I am not able rightly to apprehend".

“A user interface is well-designed when the program behaves exactly how the user thought it would.”

— Joel Spolsky

 

[stuartv]

That only means you're setting your GF High to 70 for no reason whatsoever, you could have set it to 85 from the start if you're OK with it happening mid-dive... and that is the "confusion of ideas I am not able rightly to apprehend".

“A user interface is well-designed when the program behaves exactly how the user thought it would.”

— Joel Spolsky

Are you really asserting that it would never happen that you start a dive with one intention for an ascent plan, but circumstances conspire to cause you to change your plan during the dive? E.g. by making you decide you need to get out of the water faster than you originally planned?