Matching Dive Computer Algorithms

[uncfnp]

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.

My Petrel will show remaining NDL at anypoint on the dive profile graph. Since I have been unable to transfer dive profiles from my Cressi I don’t know if it will show the same. If it does I could do a direct comparison between NDL at anypoint in time between the two computers on the same dive, up to for dives a day. Could be very interesting.

Looked but could not find the stupid little, expensive interface cable for the Cressi. May be at work.

 

[tursiops]

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.

GFlow is only applicable for dives requiring decompression. It affects the depth of the first deco stop. So it shouldn't make any difference for the NDL/no-deco dives you are looking at. I think.

 

[dmaziuk]

My Petrel will show remaining NDL at anypoint on the dive profile graph. Since I have been unable to transfer dive profiles from my Cressi I don’t know if it will show the same.

The Leo does not. I would be surprised if your Giotto does, but who knows.

Looked but could not find the stupid little, expensive interface cable for the Cressi. May be at work.

Mine's a not-so-little IR cradle with a USB port: Computers & Consoles-Giotto/Leonardo Pc Interface -- is yours different?

 

[scubadada]

1st, clean, air dive NDLs:

So, for 1st dives, PZ+, ZH-L16 ADT, and Cressi RGBM all appear to be quite similar. They may behave differently on repetitive dives

 

[dmaziuk]

That's the thing: I'm a vacation diver and we typically log 20+ dives per trip. These numbers are only relevant to the very first dive of the trip, i.e. to <= 5% of all my dives. So I 95+% don't care what they are.

 

[uncfnp]

The Leo does not. I would be surprised if your Giotto does, but who knows.



Mine's a not-so-little IR cradle with a USB port: Computers & Consoles-Giotto/Leonardo Pc Interface -- is yours different?

That is it. Hate it and the Cressi interface. Even when it was working I found it very user unfriendly.

 

[dmaziuk]

That is it. Hate it and the Cressi interface. Even when it was working I found it very user unfriendly.

"Contrary to popular belief, Unix is user friendly. It just happens to be very selective about who it decides to make friends with"

 

[dmaziuk]

I can sort of see the problem: it's hard to charge $100 for the cradle and tell the users they have to go pay for some third-party dive log program as well before they can use it. Running your own software development business, OTOH, is worse. So you quickly throw together a crapplication to bundle with your cradle that they can run and see it all works. And then anyone who cares can go find software they like.

I use subsurface myself.

 

[CandiveOz]

Depth: SF0, 1, 2

@dmaziuk thanks for listing the NDLs for the Cressi; much appreciated.

By default, the Giotto is set to Safety Factor SF0 (disabled), with options to only go up SF1, SF2, SF3.

Just to confirm, the Cressi's go to SF2 and there is no SF3?

I could do a direct comparison between NDL at anypoint in time between the two computers on the same dive, up to for dives a day. Could be very interesting.

@uncfnp what computer program are you using to do this? Subsurface?

GFlow is only applicable for dives requiring decompression. It affects the depth of the first deco stop. So it shouldn't make any difference for the NDL/no-deco dives you are looking at. I think.

Yes, that is my understanding as well, but it would be nice to know the approximate GFlow for completeness.

 

[CandiveOz]

Just getting back to the objective of the original post...

But... if I really wanted to match them up similarly, how would I do it?

As I previously indicated, as a starting point, you would look at the NDLs. From the table below with data provided by @dmaziuk and @scubadada (thanks guys ), we all agree that at the default setting the Sherwood Vision is more liberal than the Cressi Giotto. But if @divinh is happy setting the Vision to its conservative setting, then to match the computers @divinh could set the Giotto to SF1 for shallow dives (<15 metres) and to SF2 for deeper dives.

The caveat is that this applies only for the first NDL dive and square profile. NDLs may diverge on a multilevel dive due to different NDL credit for shallower depths and as @scubadada previously mentioned; repetitive dives. @dmaziuk also indicated that based on his experience, longer surface intervals brings the repetative dive NDL's closer together. I hope this kinda answers @divinh original question.