Vytec & nitrox calculations...

[jplacson]

Ok... maybe I'm missing something here but this is a quote from the Vytec manual:

"Do not round up fractional percentages. For example, 31.8% oxygen should be entered as 31%. Rounding up will cause nitrogen percentages to be understated and will affect decompression calculations."

This part I get, since this is taught in class... but this part is what confused me:

"As a safety precaution the oxygen calculations in the computer are made with an oxygen percentage of 1% + setO2%."

I'm like... HUH?!?!? I thought you weren't supposed to round up your O2 value??? And the Vytec not only rounds up the value... but ADDS 1%!!!! I checked this against the tables, and the Vytec's MOD are calculated using exactly 1% more than the entered O2 value!!!

Isn't this contradictory to the earlier warning? It's not really a big deal to me since I usually dive the tables, and I noticed this a while back and just figured they wanted to be more conservative... but isn't adding 1% a bit weird?!?! They could've just adjusted the MOD a few feet higher or something. Wouldn't adding 1% affect decompression calculations as well, and understate NO2?!?!

I haven't had a chance to do a trox dive with Vyper or Stinger users so I can't say if this applies to all Suunto computers, or just the Vytec. It's easy enough to compensate for this by subtracting 1% in your entered O2 and your MOD and MBT are adjusted accordingly, but I was just a bit curious about their conflicting statements in the manual.

 

[padiscubapro]

Ok... maybe I'm missing something here but this is a quote from the Vytec manual:

"Do not round up fractional percentages. For example, 31.8% oxygen should be entered as 31%. Rounding up will cause nitrogen percentages to be understated and will affect decompression calculations."

This part I get, since this is taught in class... but this part is what confused me:

"As a safety precaution the oxygen calculations in the computer are made with an oxygen percentage of 1% + setO2%."

I'm like... HUH?!?!? I thought you weren't supposed to round up your O2 value??? And the Vytec not only rounds up the value... but ADDS 1%!!!! I checked this against the tables, and the Vytec's MOD are calculated using exactly 1% more than the entered O2 value!!!

Isn't this contradictory to the earlier warning? It's not really a big deal to me since I usually dive the tables, and I noticed this a while back and just figured they wanted to be more conservative... but isn't adding 1% a bit weird?!?! They could've just adjusted the MOD a few feet higher or something. Wouldn't adding 1% affect decompression calculations as well, and understate NO2?!?!

I haven't had a chance to do a trox dive with Vyper or Stinger users so I can't say if this applies to all Suunto computers, or just the Vytec. It's easy enough to compensate for this by subtracting 1% in your entered O2 and your MOD and MBT are adjusted accordingly, but I was just a bit curious about their conflicting statements in the manual.

I don't dive a vytec, but for safety always round down oxygen content for calculating nitrogen loading and round up for calculating CNS or OTUs.. My guess is that they are adding 1% to the OTU/CNS oxygen exposures.

 

[jplacson]

Well, I hope you're right! I was just a bit confused since the 2 statements followed each other!

I hope that NO2 loading isn't calculated at +1%!

 

[Jai Bar]

Read Suunto's paragraph again... You round down the *Oxygen* percent, thus you actually round up *Nitrogen* percent. As a consequence, it will slightly decrease your bottom times, supposedly safer. However, Suunto decided to play safer with Oxygen *toxicity* calculations, so they add up 1%, which comes *after* you have rounded down the original O2 percent. For example, suppose you had 31.8% O2, then you entered 31% O2 --> 69% Nitrogen for deco calculations. Suunto add 1% to your 31% so they end up using 32% for O2 toxicity calculations, compared to the actual 31.8% you are breathing it is rather close, ain't it?

 

[MikeFerrara]

Plus or minus 1% on either gas just isn't going to make any difference at all. The analyzer you use to find out what your gas is isn't even that accurate.

 

[jplacson]

Ok, I just wanted to clarify on the statement since it sounded contradictory.

 

[HKRacing]

Mike F: Kind of like people having "one" analyzer so they know they have the right reading. As opposed to having two analyzers and having to guess at which mixture is the right one.