O2 Analyzer without decimal

[Sevenrider860]

Yes, their O2 calculations will be 1% higher but their NDL calculations will be 1% lower.

I never found the documentation that they reduce the O2 percentage by 1% from the entered value for NDL calculations, only that they add 1% to the entered value for O2 calculations.

The Suunto manual does state not to round up the decimal values (31.8% is entered as 31% on a Suunto)...this is the reason the PADI Manual has the "...unless the computer manufacturer literature has a different recommendation." statement.

So if I measure 31.8% and enter 31% into my Suunto as the manual states, the NDL calculations are made at 30%?

 

[The Chairman]

I was assuming it measures more accurately and rounds up/down like most electronics.

This is correct.

Isn't there something about measuring with a micrometer and cutting with an axe?

Measure with a micrometer, mark with chalk, and cut with an axe.

It's a matter of "significant figures".

If your dive requires you to be within 2%, you're cutting it too close. I teach my students to round to the nearest even number. 31 or 33 will be calculated as 32 for planning purposes. Of course, put in the actual figure into your PDC, but 32% gives you a 20% increase in time. Using the rule of 120, if I expect to dive to 60ft, I expect to be close to NoDeco limit in 60 minutes. A 20% advantage means I can another 12 minutes. Using that figure, I can easily calculate how much air I need with my SAC. After I splash, I can tell if my PDC has gone whacko or not, but since it calculates my NDL on the fly, I'm going to listen to it.

 

[Dan G]

I have never heard of the "rule of 120." Is it simply depth + NDL = 120?

 

[Sevenrider860]

I have never heard of the "rule of 120." Is it simply depth + NDL = 120?

Yes. I am pretty sure it was based on Navy Air Dive tables. I remember it from my training in '80 / '81. It was based on 60 minutes at 60 feet , 30 minutes at 90 feet. The other depths had some variations (48 minutes at 70), but the 120 rule was easy to remember.

 

[broncobowsher]

To the OP and the original post, find a different analyzer to comply with the PADI rules.
To the rest of the world, you are not going to get a basic Nitrox analyzer to calibrate down to a tenth of a percent. Most of the basic Nitrox analyzers you can slightly tweak the flow rate and how tight you press the ball against the tank and move the reading a full percent point.

As for the rounding up/down, depends on what you are trying to do. MOD, round up. Deco, round down.
Now factor in the science isn't a knife edge, but a blurry transition. In the real world there really isn't anything gained with that extra decimal point.

Calibrating a Nitrox analyzer in air? Ever try that then put it on a bottle of 100% and see what you actually get back?

 

[dberry]

I have never heard of the "rule of 120." Is it simply depth + NDL = 120?

Yes. Some folks will say it should be 140 at some depths, but I just use 120 as a "sanity check", not for careful planning.

 

[Sevenrider860]

Calibrating a Nitrox analyzer in air? Ever try that then put it on a bottle of 100% and see what you actually get back?

Calibrated in air, put it on a bottle of 100% and it returned 99.2%. I got what I was expecting. Were you expecting a different result?

https://youtu.be/kVr4Aj6oapk

 

[The Chairman]

I have never heard of the "rule of 120." Is it simply depth + NDL = 120?

Yes. But please use it for planning only. I used to dive with that as my only guide, even to guessing my depth based on a red ribbon tied to my harness. Then it got complicated albeit safer with tables and a real depth gauge. The advent of the PDC makes it easy, but the rule of 120 is still a quick shortcut for planning. You don't need to blindly follow that PDC, if your using the rule of 120 as a sanity check.

 

[PR_SMITH]

I have never heard of the "rule of 120." Is it simply depth + NDL = 120?

It's 120- max planned depth=NDL. As mentioned, it's just for rough planning.

 

[The Chairman]

Calibrated in air, put it on a bottle of 100% and it returned 99.2%. I got what I was expecting. Were you expecting a different result?

You are golden.