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

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I have learned a little bit more about the G2 Tek algorithm. I am sure it changes no opinions on who will or will not use it, but I do like to understand how the computer algorithm works and share that information.

Deco schedule does not match Shearwater or Scubapro HUD
While the G2 Tek is more conservative than the Shearwater, it is not because they have implemented an incorrect or wrong ZH-L16C + GF algorithm. It is the inputs they chose to use for the algorithm that cause the differences.

I know this is not a great analogy, but the Pythagorean theorem is a2 + b2 = c2. If I use a = 1.1 and b = 2 while another person uses a=1 and b=2, it is not that the equation is wrong, it is that the inputs to the equation were different. I believe this is what is happening with the ZH-L16 algorithm used by Scubapro. Scubapro does document this in the user manual. It is in the Altimeter section of the user manual. I have copied the text from the section below, and made the important text bold.

"Barometric pressure is variable, changing with weather and atmospheric pressure at any particular elevation. Dive algorithms use altitude classes which are directly derived from barometric pressure. Displayed altitude is determined based on the current barometric pressure and is therefore a relative value. "

Scubapro uses altitude classes as the input into the decompression algorithm. They use the top end of the altitude class. So if the Altimeter is measuring pressure at Sea Level, you are in altitude class C0 and the input into the algorithm is 1,000 meters. Playing around in Multideco and changing the Dive Elevation depth between 0 and 1,000 meters does seem to give run times with a difference similar to what I saw when I performed an actual test dive with the Shearwater and G2 Tek.

Altitude Class.jpg


Dive Planner shows shorter NDL times.
There is a double hit here. The dive planner is using the current altitude class (1,000 meters at sea level) and the G2 Tek dive planner assumes the dive starts at the depth indicated. The G2 Tek dive planner does not calculate a descent rate like the Shearwater and Garmin computers do.

Scubapro HUD is different than the G2 Tek
This has been confirmed. Scubapro HUD does not use altitude classed and uses the measured barometric pressure.


An interesting note...
For anybody that liked the SEABEAR computers (Scubapro bought the company in 2015), the founder, Dr. Arne Sieber stayed with Scubapro as the R&D Manager for Scubapro Dive Computers until 2017. Dr. Sieber founded Oxygen Scientific, which has solid state O2 sensors and dive computers with wireless PO2 and Air integration. Halcyon will sell them in their Symbios CCR ecosystem.
 
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?

Getting out faster than originally planned means getting out with less gas loading than originally planned.

Changing GF from 70 to 85 mid-dive does the exact opposite.

There's a bit of a difference there.
 
Getting out faster than originally planned means getting out with less gas loading than originally planned.

Changing GF from 70 to 85 mid-dive does the exact opposite.

There's a bit of a difference there.

:bigpalm:
 
Getting out faster than originally planned means getting out with less gas loading than originally planned.

Changing GF from 70 to 85 mid-dive does the exact opposite.

There's a bit of a difference there.
you do know how wrong that statement is right?
 
Thanks @Sevenrider860

I can't understand why Scubapro would use an elevation of 1000 m when diving at sea level with the G2 Tek rather than the actual barometric pressure as used with the HUD. Does the Luna 2.0 work like the G2 Tek?

Shearwater uses the actual barometric pressure. This can easily be demonstrated by using the NDL planner at different barometric pressures. I was interested in this when I first got my Teric and constructed a spreadsheet covering between 985 and 1028 mbar.

1710356369148.png
 
you do know how wrong that statement is right?

Only if you don't ride your GF all the way to 85 and surface with 70 as originally planned. In which case: why did you you change it mid-dive, "because you can"? (*)

*)Why does a god lick its junk?
 
Scubapro uses altitude classes as the input into the decompression algorithm. They use the top end of the altitude class. So if the Altimeter is measuring pressure at Sea Level, you are in altitude class C0 and the input into the algorithm is 1,000 meters.

View attachment 831577
This is so stupid. They have the surface pressure, yet they chose to ignore it in favor of rounding to the next 1000m? What is their justification for this?

If they were consistent in their logic, they should also round pressures at depth to the next 10 ft. level. Congratulations, they've reinvented PADI's The Wheel.
 
There is no magic transferred to the diver by using a particular computer, your personal physics are what they are so for many of us all computers are a touch more consertive than necessary others like a friend on Truk get bent using a Suunto, so no magic avoid riding the sharp edge until you know what works for YOU.
 
you do know how wrong that statement is right?

(With thanks to @scubadada) yes: if you cut your dive short early enough, when you are still on-gassing, you can indeed surface with less gas loading than originally planned. So that statement is indeed not universally true.
 
:rofl3: :rofl3: :rofl3: OK, I officially need a day off. I did of course mean "more" when I typed "less", and it took me three -- count 'em -- re-reads to see that.

:facepalm:
 

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