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If I have understood what he wrote correctly (which is always suspect), the contrasting (and preferred) behavior that one would find in a Petrel is that if one wanted to do one's last stop at 20', a deco ceiling of 10' would be cleared by stopping at 20' and waiting just a bit longer than the 10' stop requires

Only correction: Per Buhlmann ZHL-16C, my understanding is that staying at 20ft during the "10ft stop time" should yield equaldeco obligation on O2...not slightly more. So 20 minutes on O2 at 20ft is the same as (for example) 7min at 20ft and 13min at 10ft as long as you don't breach the ceiling.
 
Only correction: Per Buhlmann ZHL-16C, my understanding is that staying at 20ft during the "10ft stop time" should yield equaldeco obligation on O2...not slightly more. So 20 minutes on O2 at 20ft is the same as (for example) 7min at 20ft and 13min at 10ft as long as you don't breach the ceiling.

Just FYI, I ran a few deco plans on both MultiDeco on my laptop and on PastoDeco on my Android tablet.

On both platforms, some profiles resulted in a slightly longer deco with last stop set to 20' versus a last stop of 10'. Some were the same, which I would chalk up to rounding error. I was just running a simple square dive, 130', 12 - 15 minutes on EAN28 with 100% for deco. Last stop at 20' for that dive gives 1 minute longer run time than last stop at 10' (12 or 15 minutes).

IOW, both of the software packages I checked (using ZHL16-C, GF 35/75 on one and 20/85 on the other) did not agree with you on deco at 20' being equal to deco at 10'.

Being quite a large pressure difference between the two, it doesn't make sense to me that they would be equal, either. If deco at 60' isn't the same as deco at 50', why would 20' and 10' be the same? There's a much bigger pressure gradient between 10' and 20' than 50' and 60'.

Of course, this doesn't change the fact that hanging at 20' should reduce the required stop time at 10', though not in exactly a 1:1 ratio.
 
100% O2 is 100% o2 regardless of what depth you are at, the depth is there to keep the bubble size down, but the gradient that the o2 is fighting to push the nitrogen out should theoretically be the same regardless of depth because there is no other gas being used.
 
100% O2 is 100% o2 regardless of what depth you are at, the depth is there to keep the bubble size down, but the gradient that the o2 is fighting to push the nitrogen out should theoretically be the same regardless of depth because there is no other gas being used.

Okay, I got an A in college chemistry. I've read Deco for Divers. I knew that. It's been a few months and I had to think it through again to remind myself exactly why that is and I've got it now.

To answer my own earlier question, the difference between 50/60 feet matters where 10/20 doesn't because at 50/60 you will have some amount of N2 in your deco gas. And any N2 in the deco gas means the depth affects the partial pressure of N2 in that gas. A deeper depth means a higher ppN2 in the gas which means deco is slower. But, once you get to 20' and switch to 100% O2, the ppN2 is 0, no matter what depth you're at (0 times anything is still 0), which means N2 off-gasses at the same rate no matter the depth.

So, any idea why these different dive plan tools show a faster deco (shorter run-time) when you ascend to 10' versus hanging at 20' (on 100%)?

---------- Post added January 13th, 2016 at 05:35 PM ----------

So, any idea why these different dive plan tools show a faster deco (shorter run-time) when you ascend to 10' versus hanging at 20' (on 100%)?

I think I have figured it out. And I note now that the MultiDeco plan actually has the deco that includes the 10' stop taking 1 minute longer than with the last stop at 20'.

I think it is because the software only does stops in full 1 minute increments.

So, with a last stop at 20', the program calculates > 1 minute of deco required, but less than 1:40. So, you stop at 20' for 1 minute, then complete the rest of the deco during the 0:40 ascent from 20' to the surface.

But, when you have a last stop setting of 10', the program stops you at 20' for 1 minute, then has you ascent to 10' to complete your deco. You only need 40 seconds (or less, but probably more than 20 seconds), so it wants you to stop at 10' to complete it. It only allows whole minute stops, so you have to stop for 1 whole minute even though you don't need a whole minute to finish deco. And then it shows 1 more minute to get to the surface because, obviously, it takes > 0 time to go from 10' to the surface.

I'm guessing that if the app allowed me and I set it to generate deco stops down to the second, instead of in whole minutes, then the plans would be the same.

---------- Post added January 13th, 2016 at 05:43 PM ----------

I'm slated to receive the H3 I ordered tomorrow. I have a plan in mind to try and test what Victor said, without getting in the water and ruining my ability to return the H3 for a refund.

The latest H3 firmware has a dive planning tool that supposedly allows you to enter multi level dives.

So, my thinking is to plan a dive that results in a 20 minute (more or less) deco stop at 10' on 100%.

If I then add a second level to my dive of 20' for 20 minutes on 100%, the resulting dive plan in the simulator should yield the same run-time. If the H3 works like it should.

If the current firmware still works the way Victor described, then my dive simulation should result in a dive that ascends to 20' for 20 minutes and then stops at 10' for another 20 minutes.

Right?
 
Being quite a large pressure difference between the two, it doesn't make sense to me that they would be equal, either. If deco at 60' isn't the same as deco at 50', why would 20' and 10' be the same? There's a much bigger pressure gradient between 10' and 20' than 50' and 60'.
The difference in 50v60 and 20v10 is the PN2. Inhaled PN2 at 20ft is the same as it is at 10ft when you're diving pure O2. So, it should be a 1:1 ratio.
 
At 3m/min travel time, 6m takes one minute longer to surface than 3m. There is no difference in PN2 at 3m and 6m. This is basic decompression diving.
 
This thread seems to be the compendium of H3 knowledge and a place where it has received some support, so I figured I'd ask here.

Basically, what about the info in this thread?

http://www.scubaboard.com/forums/co...analyzers/520314-step-up-dive-computer-2.html

What victorzamora has posted there about his experience with the H3 makes it sound like the H3 has a serious issue with tracking decompression obligations. 2 examples of what he said:

- stopping at 20' does not shorten the time the H3 requires at 10' at all.

- 20 minutes at 50' don't affect the time required to stop at 30'.

If I have understood what he wrote correctly (which is always suspect), the contrasting (and preferred) behavior that one would find in a Petrel is that if one wanted to do one's last stop at 20', a deco ceiling of 10' would be cleared by stopping at 20' and waiting just a bit longer than the 10' stop requires. And, when ascending from some deeper depth where you have incurred a deco stop at 30', spending 20 minutes at 50' would (substantially, I think) reduce the time required to be spent at 30'.

I emailed Sub Gravity earlier today to see what they have to say about this behavior. I have not heard back yet, but it has only been a few hours. But, really, a response here (on in the linked thread) would potentially help a lot more people than just me.

I ordered an H3 yesterday. If I can't get some verification that this behavior is resolved or some explanation of why victorzamora experienced these things, I think I will have to return the H3 for a refund. There is no way I want to do deco dives with a computer that won't let me do my final stop at 20 or 30 feet if I want to and still clear my final deco obligation in the time that would be predicted by ZHL-16C and my GF settings.

The H3 is more than happy for you to do your final stop at 20', 15', or 10' or 11' or 12' for that matter. It will adjust the deco time required accordingly, just like any other technical diving computer.
 
The H3 is more than happy for you to do your final stop at 20', 15', or 10' or 11' or 12' for that matter. It will adjust the deco time required accordingly, just like any other technical diving computer.

Randy, from what Victor said about the way it worked when he demoed an H3, are you able to say that that is a known behavior of a previous version of the firmware, which is fixed in the current version?
 
I received the H3 today. I used the Dive Simulation tool (a new feature in the latest firmware) to run this simulation:

GF95/95
Air + 100% O2

Descend to 200' for 9 minutes. This generates a first stop at 20' of 1:00 and a stop at 10' of 3:00.
I then added a level of 20' for 10 minutes. This gave me a normal ascent and 4 minutes at 20'.

As the sim runs (at 10x speed on time), the computer prompts for a gas switch just as it would during a real ascent. I switched to O2 at 20' and "hung" there while watching the screen showing the deco stops. It started with a display of 3:00 at 10' and, as I "hung" at 20', the 10' stop time ticked down and then eventually, when I cleared all deco, the screen showing the ascent plan went away and left me on the dive profile screen (and still at 20' in the simulator with the main dive screen now showing me back into NDL mode).

If I assume that doing the same thing in real life would result in the computer behaving the same way, then it certainly seems like Randy is right and the behavior Victor saw before is fixed.
 
I received the H3 today. I used the Dive Simulation tool (a new feature in the latest firmware) to run this simulation:

GF95/95
Air + 100% O2

Descend to 200' for 9 minutes. This generates a first stop at 20' of 1:00 and a stop at 10' of 3:00.
I then added a level of 20' for 10 minutes. This gave me a normal ascent and 4 minutes at 20'.

As the sim runs (at 10x speed on time), the computer prompts for a gas switch just as it would during a real ascent. I switched to O2 at 20' and "hung" there while watching the screen showing the deco stops. It started with a display of 3:00 at 10' and, as I "hung" at 20', the 10' stop time ticked down and then eventually, when I cleared all deco, the screen showing the ascent plan went away and left me on the dive profile screen (and still at 20' in the simulator with the main dive screen now showing me back into NDL mode).

If I assume that doing the same thing in real life would result in the computer behaving the same way, then it certainly seems like Randy is right and the behavior Victor saw before is fixed.

This sounds very exciting!!! When are you diving for real with this computer??? How was the display?
 

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