Cressi Leonardo - MOD vs PO2 discrepancy

[delta-v]

Till such time that Cressi updates the Leonardo user manual, here is a summary for divers who may visit this thread looking for answers:

The discrepancy
1. When entering a Nitrox mix into the Leonardo, the displayed MOD will be shallower than what you expect. This is because the Leonardo adds 0.8% to your Nitrox mix for MOD calculation (e.g. 32% becomes 32.8%).

2. If you then go into PLAN mode, to determine your NDL, you may not be able to reach your target depth on the planner if it exceeds the modified MOD for your Nitrox mix.

3. This modification is apparently not uncommon for recreational dive computers, but at the time of writing Cressi does not disclose this information in the Leonardo user manual.

How does this impact you
If you are using the Leonardo to determine MOD for marking your cylinders and planning your dives, then you need to be aware of this discrepancy. Your MOD and dive plan may be significantly different from other divers in your group who are diving the same Nitrox mix.

The real MOD can easily be calculated by a simple formula, which you would have learned as part of your EANx course.

The real NDL is not so simple to calculate. You can use EANx tables if you have them, or dive planning software. Else, just dive the Leonardo and keep a close eye on the NDL time remaining.

 

[runsongas]

0.8% seems like a weird number. at least 1% sort of makes sense as a whole number.

 

[delta-v]

That is true for really small values of 2, with really large values of 2: 2 + 2 = 5

I wasn't quoting literally, but thanks hehe : )

 

[delta-v]

0.8% seems like a weird number. at least 1% sort of makes sense as a whole number.

This whole deal is weird.
Imagine paying for a precision instrument which thinks you're an idiot and can't be trusted with real data.

 

[Jcp2]

You mean like the speedometer on a modern car?

 

[delta-v]

Sadly yes.

To be honest, I had no idea it was this bad. My first computer was an Aladdin Tec 2G, which was given away when I started trimix. Then some X1s, Shearwaters, and the latest addition are some TDCs (plural because I use them for tec students too).

I have never known life on the other side of the (dive computer) train tracks.

I always knew that Sunntos were creepy, like a nanny who wouldn't let go of you, but this MOD modification is just unacceptable.

 

[Centrals]

I never found any computers or bottom timers that I have been using registered identical depth!
My ancient Aladin Pro Nitrox has the nitrox setting in 2% increment and never have any problem whatsoever.
The trick is dive conservatively.

 

[Rooster59]

My guess would be Cressi adjusts the oxygen percentage as a way to account for errors in the measurement given by the depth sensor and / or errors in the gas mix. 0.8 / 32 is 2.5%. This would be safe real world engineering versus the exact numbers in the model.

 

[poliver319]

Yes, so we disabled the Deep Stop and the Dive Safety Factor at the outset.
Following your reply, I asked the student to change SF back to 1 and 2 and run the PLAN mode again.
Unfortunately the max depth does not change - there's still a significant discrepancy.

I've also ruled out saltwater/fresh water conversion (the Leonardo doesn't have this as an option).
Will write Cressi directly.

Did you ever get a response from Cressi? I'd be interested in hearing what they had to say