Matching Dive Computer Algorithms

[dmaziuk]

As for the quote from @Freewillow he stated that he dived with the Cressi Leonardo 100 times. Why would I question his experience or integrity?

Because his statement the leonardo "does not recalculate" when you come up is rubbish, that's not how any dive computer works. You'd have to look at his 100+ logs to see what was actually going on on his 100+ dives.

Same goes for picking four random points along three random profiles and calling it "a study". DSAT gives you longer NDLs, we knew that already, trying to read anything more into those "studies" is rubbish.

since you own a Cressi and you are a frequent participant on these forums, it would be great if you could post the NDL's of the Cressi default and Conservative settings like @scubadada so we can all gain a better understanding of these computers. I look forward to your table.

Why would I ever keep the record of my NDLs? I dive to have fun ad as long as my computer does not limit my fun, I don't give a toss about the exact number on the screen as long as it greater than zero. I can tell you that dives I surface from with less than 99 on NDL display are square profiles with 40-minute SIs. For splashing around Caribbean reefs 3-4 hours a day for 7-9 days straight, my computer works just fine.

 

[scubadada]

Hi @dmaziuk

I think what @CandiveOz meant is that you could simply list the NDLs by mix and depth from the planning function on your computer, similar to what I did in post #12. It would give those of us who do not dive Cressi computers a chance to make a comparison. I would be willing to bet that the clean, 1st dive NDLs would not be much shorter than those of other deco algorithms. As frequently discussed, this would not give any insight into the influence of repetitive dives.

Of course @divinh could set his Vision on DSAT +C and check out the NDLs between his Sherwood computer and his Cressi computer himself

 

[dmaziuk]

Hi @dmaziuk

I think what @CandiveOz meant is that you could simply list the NDLs by mix and depth from the planning function on your computer, similar to what I did in post #12.

And it would be pointless without also including the length of the surface interval after which you pressed your "plan" button. And with an RGBM computer it would also be pointless without specifying overall ascent rate from previous dive. As you yourself said in that post, RGBM penalizes for short SIs and rapid ascents (although I would argue it's more like it promotes longer safety stops, but that's semantics) So what does that table tell you, really? Other than what you already know: "RGBM is less liberal".

 

[scubadada]

And it would be pointless without also including the length of the surface interval after which you pressed your "plan" button. And with an RGBM computer it would also be pointless without specifying overall ascent rate from previous dive. As you yourself said in that post, RGBM penalizes for short SIs and rapid ascents (although I would argue it's more like it promotes longer safety stops, but that's semantics) So what does that table tell you, really? Other than what you already know: "RGBM is less liberal".

No, you would run all the plans at one time on a clear computer, no dives. It would give you the longest, default, NDL for each depth/mix

 

[CandiveOz]

Just to clarify, all I'm looking for is the NDLs for the computer based on its default setting and its conservative factors. For example, I was interested in learning more about the Scubapro G2 so I borrowed one from a dive club member and took it for a dive. I also jotted down the G2 NDLs for each microbubble level (conservative factors). Attached is the table if anyone is interested. The depth is in metres and the 3 numbers represent the deco stop depth, deco time, and total ascent time. I open my request to anyone who has a Cressi and has the time to put a similar table together. Personally I find this information useful. And I apologise to @dmaziuk with my request if he doesn't have the time or inclination to do it.

 

[uncfnp]

I could go you one further if my Giotto download kit worked. I have dove both a Giotto and a Petrel for several years now with the Cressi at 0 SF and the Petrel in both VPM and GF’s settings. I haven’t tried the link for a while now. I may give it another go tomorrow. If it works I can upload actual dive profiles to compare dives. Otherwise its just casual observations on my part.

I can tell you that it is interesting how often over the years that I have heard divers lament over the conservatism of RGBM and yet I now dive the Petrel as primary and the Cressi as backup and I don’t think I have once put the Cressi in deco even when I I have had the Petrel down to minutes of NDL at 50/80.

 

[divinh]

Just to clarify, all I'm looking for is the NDLs for the computer based on its default setting and its conservative factors. For example, I was interested in learning more about the Scubapro G2 so I borrowed one from a dive club member and took it for a dive. I also jotted down the G2 NDLs for each microbubble level (conservative factors). Attached is the table if anyone is interested. The depth is in metres and the 3 numbers represent the deco stop depth, deco time, and total ascent time. I open my request to anyone who has a Cressi and has the time to put a similar table together. Personally I find this information useful. And I apologise to @dmaziuk with my request if he doesn't have the time or inclination to do it.
View attachment 498327

The G2 has conservative factors going from P0 to P9? Is that how the table is read? And the dive planner gives deco depth and time as well?

 

[CandiveOz]

The G2 has conservative factors going from P0 to P9?

Actually Scubapro uses "L" for Microbubble Levels L0 - L9 with L0 being the default. I used "P" probably because I had used a copy of another one of my spreadsheets for Suunto which uses "P" for Personal settings (my mistake). Of course Cressi uses SF (Safety Factors).

So the short answer is yes, the Scubapro has 10 levels but there is a unique distinction between the Scubapro computers and other brands. With other brands, if you set the conservative factor, the NDL is shortened. And if you go into deco based on this conservative factor, but do not follow the decompression profile, the computer will lock you out. This will occur even if your dive under its default setting would have been within its NDL limits.

With Scubapro, if you set the G2 to L9, its most conservative setting, but ignore the microbubble level stop (its not a deco stop) the computer then cascades to the next level (in this case L8). It will continue to do this until L0 which is now your decompression stops. Ignore these and the computer locks you out. So with the Scubapro, you may plan to dive at a particular microbubble level but due to unforeseen events need to cut your dive short and you end the dive with a lower microbubble level.

And the dive planner gives deco depth and time as well?

Yes, the dive planner in the computer gives deco depth and time for the first deco stop in a decompression profile. Take P9 (L9) at 57 metres. Although this is a microbubble level stop, it indicates a stop at 9 metres for 2 minutes. But note, the total ascent time is 26 minutes so there are probably stops at 6 and 3 metres as well. During the dive, the G2 will tell you if you are at a microbubble level stop or an actual decompression stop. To gain more of an understanding about the Scubapro computers, you may want to download the G2 or Galileo user manuals and go through them. They are quite different to other dive computers.

 

[CandiveOz]

I don’t think I have once put the Cressi in deco even when I I have had the Petrel down to minutes of NDL at 50/80.

@uncfnp thanks for you input. That has been very helpful and one of the reasons why I like to know the NDLs of different dive computers. Its allows me to back solve (in a rough way) what the equivalent GFhi would be (at least on the first dive). To work out the GFlo is a bit more difficult because you are trying to match a particular deco profile from a specific depth. For example I own a Tusa IQ750 which runs PZ+ and at its default setting its GFhi is around 85. If I set it to its conservative factor, the GFhi drops to around 75. So based on your diving, the Cressi is probably a GF 50/80 computer (or thereabouts). By back solving the gradient factors of my computer I get a feeling for what I am use to so when I decide to upgrade to a computer with gradient factors I know what setting I will be comfortable with. Thanks again

 

[dmaziuk]

If it works I can upload actual dive profiles to compare dives.

Logs are easy, I could upload mine by yesterday. But they don't include the calculated NDLs. Getting what OP asked for out with a single button is a PITA.

Clean Leo, on air, altitude 0. On its 2-digit NDL display 99 is "no NDL".
Depth: SF0, 1, 2
9 : 99, 99, 99
12 : 99, 98, 83
15 : 68, 60, 54
18 : 49, 44, 40
21 : 37, 33, 30
24 : 28, 26, 22
27 : 21, 19, 17
30 : 17, 15, 13
33 : 14, 12, 11
36 : 11, 10, 9
39 : 9, 8, 7
42 : 7, 6, 6
45 : 6, 5, 5
48 : 5, 4, 4
- does not go deeper.

Sorry (not), I'm not sufficiently interested to repeat the exercise for all altitude settings and EAN mixes.