Garmin Descent Mk2 vs Cressi Leonardo

[homerdoc]

Today we dove the Speigal Grove in Key Largo. I had recently gotten my daughter and wife Garmin dive watches (the Mk2 and the smaller one, cant remember the name).

As we were diving, they got worried and did the check NDL sign - I looked and I was at 20 minutes and I had been deeper than them, so I was like what is up? My daughter was wearing her old Cressi and her Garmin - and swam over to show me. Where I had 20 minutes, she had 7 on her Garmin and 20 on her Cressi.

Is this just where one watch is using a different algorithm? They were all set on air, so they were all set the same.

One cool thing - there garmins started alerting at 10min NDL.

 

[Outbound]

The Cressi uses RGBM, which is a very conservative algorithm. Most Suuntos use it as well. Garmin uses Buhlmann, I believe. So not surprising to see the discrepancy.

 

[Belzelbub]

What were you using? Sounds like yours matched your daughter's Cressi.

I'd definitely have a look at how you had the conservatism set on both computers. The Garmin uses Buhlmann with GFs, and also has custom GFs. I usually dive with my Perdix set at 40/85.

I'd also look at the gas programmed. If they were diving EAN, but had the Garmins set to air, that could account for it as well.

The discrepancy from the different algorithms isn't surprising, but the direction of the discrepancy does seem to be. The only thing I can think of is that either the gas was wrong and/or the Cressi was set to it's most liberal setting while the Garmin was set conservatively.

BTW, the smaller Garmin is either the MK2S or G1.

 

[Outbound]

Sorry, I just realized that I misread the original post. I mistakenly thought the Cressi was reading 7 minutes while the Garmin was reading 20. Given how conservative RGBM is, that might make sense. But the other way around? That seems odd to me if all the other settings (gas, conservatism) were the same.

 

[CycleCat]

Surprised that 7 & 20 minute NDL wasn't switched around. You must have the Cressi on its least conservative setting and the Garmin dialed way up to high.

 

[homerdoc]

Yeah - my cressi matched her cressi - and both their garmins matched. The garmins out of the box must have been set more conservative - Will look at how to get them to match the cressi when I get back home - been diving the cressi's for a long time so I trust them, but the girls wanted the new watch.

The Cressi also matched the the NDL the dive master had.

It does seem pretty cool built in compass and such.

Thanks for all the replies.

 

[inquis]

The Cressi uses RGBM, which is a very conservative algorithm.

Yes and no... Clean NDL times down to 100 ft on RGBM are equivalent to Buhlmann+GF x/95, which is pretty liberal. The "conservative" reputation of RGBM shows up on repetitive dives.

 

[Esprise Me]

Yes and no... Clean NDL times down to 100 ft on RGBM are equivalent to Buhlmann+GF x/95, which is pretty liberal. The "conservative" reputation of RGBM shows up on repetitive dives.

That's consistent with my experience. I did a liveaboard in Turks & Caicos, where we did 5 dives per day, many to triple digit depths, over a week. I wore both my Cressi Leonardo and my Shearwater Teric (which runs Buhlmann also.) On most dives, the Teric was showing more NDL; it particularly stood out in terms of how much "credit" it gave me for coming up to the top of the wall (ascending from ~100ish to ~40ish feet.) But sometimes on the first dive of the day, just when I'd first hit my max depth, I noticed the Cressi giving me more time.

 

[stepfen]

I dive a divecomputer.eu computer running Buhlmann and as a backup a Cressi Newton (same RGBM algorith with Leonardo etc). Usually 30/70 or 30/80 in Buhlmann and no conservative factor (SF or whatever it is called set to 0) in Newton. Both DCs always set to match the mix I dive (usually EAN around 30% but occasionally air too).
It is very common for the first couple of dives the Buhlmann to be running out of NDL 10-15 minutes earlier than Newton. Actually it happens in all the dives that I dive near MOD.
Newton (RGBM) is getting (occasionally very) conservative from the 3rd dive onwards. That's how they've got their conservative fame. During dive vacations and LoBs (where usually people do multiple dives a day) this can get very frastrating.

Another major difference between the two is that if you reach deco (better not if you are not trained and have proper planning and equipment), Buhlmann clears it much easier/faster (usually on the way to the first stop if it just a few minutes), while RGBM keeps adding deco time any time the diver is below a few feet from the ceiling.

I hope these help.

 

[d^2b]

It is very common for the first couple of dives the Buhlmann to be running out of NDL 10-15 minutes earlier than Newton. Actually it happens in all the dives that I dive near MOD.
Newton (RGBM) is getting (occasionally very) conservative from the 3rd dive onwards.

That matches my experience with a Shearwater peregrine (Buhlmann) and a Suunto Zoop Novo (RGBM). I have since replaced the Zoop Novo with another computer running Buhlmann, but my dive buddy is still diving a Zoop Novo, so I sometimes notice they are disagreeing, in both directions. Of course with my buddy it is less clear that the computers are diving the same profile.