Need clarification on my dive computer settings and algorithms (vs Dive Planner)

Peter Sims · Sep 3, 2013

Hi guys,

I am trying to figure out my computers now that I'm doing my Nitrox course.

I have two computers: One a simple Veo1.0 which has the PZ+ and DSAT algos
The other a Oceanic Datamask that runs modified Haldanean (DSAT).
I'm also comparing this against the recreational dive planner which is 20min before deco diving on air (30m) and 9min (40m) .

Veo1.0 (PZ+)	30m	Air 16min NDL	Ean32 27min
	39m	Air 9min	Ean32 15min
Veo1.0 (Dsat)	30m	Air 20min	Didn't calculate
	39m	Air 11	Didn't calculate
Datamask	30m	Air 20	EAN32 31min
	39m	Air 11	EAN32 18min

The question I ask is what should I have my Veo1.0 set at? And should I be turning on conservative factor on my datamask? Are the recreational dive charts liberal as they are???

I think this might help a lot of people out there (as I can explain it to my buddy who runs a VT3)

Thanks in advance guys

tphelps · Sep 3, 2013

The DSAT is a more "liberal" algorithm while Z+ is more conservative. There is nothing wrong with being conservative, I mean it is just being safer. (But don't get me started on Suunto's RGBM algorithm...grumble grumble grumble) If I were you, I would run Z+ with your data mask because they have similar conservative factors. If you want to run additional conservative factors that is your prerogative, I personally don't think you need to because both are already very conservative. Dive charts are meant to be very conservative so no, not that I am aware of.

Oh and BTW, I plugged in EANx32 with a max PO2 of 1.4 on my Oceanic OCS - DSAT dive planner: For 100 feet I got 30 minutes NDL. 39m is past the 1.4 max PO2 so I didn't plan for that one. Have fun on your nitrox course!

scubadada · Sep 3, 2013

My primary computer is a VT3 and my backup is a Geo2 and a SPG. The VT3 runs only DSAT, the Geo2 runs DSAT and PZ+ (same as your 2 computers). I run both with DSAT without conservative factor so that they match and are in sync. The conservative factor simply runs using one altitude level higher than where you are. The liberal/conservative discussion can go on forever, it's a personal decision, I appreciate the relatively liberal DSAT algorithm.

Steve_C · Sep 3, 2013

32% at 39 meters is almost 1.6. Definitely past 1.5.

scubadada · Sep 4, 2013

The Oceanic computers can be set for a PO2 max up to 1.6 and will calculate dive times in the planner up to the MOD based on the PO2 set. At PO2 of 1.4, MOD for 32% is 111 ft, 34 m. At a PO2 of 1.6, MOD for 32% is 132 ft, 40 m. I would imagine most set their PO2 max at 1.4, but not everyone

Steve_C · Sep 4, 2013

By the way there is a free ap for the iphone called Diving MOD. You set max PO2 in increments of 0.1 and O2 % in increments of 1% and it gives max depth in metric or imperial. I find it very helpful. I like a max PO2 of 1.3 and when I picked up my tanks at the LDS they had given me a mix that was slightly richer than I had requested for a deeper dive. Quick check showed I was at 1.3+ if I played in the sand so I took the tanks.

I find it handy (and yes I have compared it to accepted tables) since the iphone is always with me while tables are not.

Peter Sims · Sep 5, 2013

Thanks for the replies guys.

I suppose what I was really getting at was say I set my PO2 at 1.6 (the limit) and was say in Truk doing a wreck and I was around 38-39 Metres. On the DSAT setting would I be seriously risking myself staying down there? (For the entire time up until the decompression limit (obviously leaving before it hits))

45mins at 1.6 PO2 is the limit according to the paper work.

That is the part which confuses me.

Steve_C · Sep 5, 2013

There are nitrogen limits (NDL) before deco
There are oxygen limits (the 1.6 bit)
There are total oxygen exposure limits

Need to be specific what you mean by limits.

Just remember that it is all probabilities and they vary by the day and dive. The closer you are to the limits and the more you push them the less margin of safety you have. Just because you are just below a limit does not mean you are 100% safe. It's ALWAYS Russian roulette. Do you want 1 bullet in a gun with 1,000 chambers or a gun with 1 bullet in 10 chambers?

scubadada · Sep 5, 2013

I generally agree with Steve. Nitrogen exposure is generally easy to deal with, stay out of deco or do the mandatory stops and run a small risk of getting bent. Oxygen exposure is another matter, exceed the recommended PO2 of 1.6 atm or exceed the daily exposure limit from the NOAA tables and run a small risk of oxygen toxicity, a seizure, and a likely outcome of death.

Many are appropriately concerned about their nitrogen exposure, many fewer are aware of and appropriately concerned about their oxygen exposure. There is a very significant difference in the outcome.

Peter Sims · Sep 5, 2013

scubadada:
I generally agree with Steve. Nitrogen exposure is generally easy to deal with, stay out of deco or do the mandatory stops and run a small risk of getting bent. Oxygen exposure is another matter, exceed the recommended PO2 of 1.6 atm or exceed the daily exposure limit from the NOAA tables and run a small risk of oxygen toxicity, a seizure, and a likely outcome of death.

Many are appropriately concerned about their nitrogen exposure, many fewer are aware of and appropriately concerned about their oxygen exposure. There is a very significant difference in the outcome.

Thanks, that's exactly the information I was hoping for. And a great saying. So basically its far riskier to go closer to the oxygen limit then actually hit the nitrogen limit.

So basically when using Nitrox, set your personal limit at 1.4 PO2 and use the mix that gives you that figure at the depth you want to dive. I suppose that's why it's called a Maximum Operating Depth.

Thanks Steve for your information also!

Need clarification on my dive computer settings and algorithms (vs Dive Planner)

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