Sherwood Wisdom Default FO2 Question

Just got my brand spanker Wisdom2, which is lovely, and have read manual, which is easy to read, but am a little confused by the following:

When set ON, 10 minutes on the surface after the dive FO2 is displayed as 50 and further calculations are based on 50% O2 for Oxygen and 21% O2 for Nitrogen (79% Nitrogen) unless you set the FO2 before the dive. FO2 continues to reset to the FO2 50% DEFAULT after subsequent repetitive dives until the unit shuts Off, or the DEFAULT is set OFF.

When set OFF, the FO2 Value remains set at the last seen point selected for the remainder of that Activation Period

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What does this bit mean - "further calculations are based on 50% O2 for Oxygen and 21% O2 for Nitrogen (79% Nitrogen)"? I'm sure it's fairly simple, I just need a little clarification.

Thanks


Rick

Basically this is a fail-safe feature.... With this setting ON, you have to set your mix after every dive whether air or nitrox. If you do not set it manually and plan on making another dive before the unit shuts off, it defaults to the settings you mention which will give you a very short and limited subsequent dive.

Why?The "50% O2 for Oxygen and 21% O2 for Nitrogen (79% Nitrogen)" is basically two worst case scenarios (w/in limits).

'50% O2 for Oxygen' -- You were diving a 50% mix of Nitrox (big Oxygen uptake)
'21% O2 for Nitrogen'-- You were diving air (big Nitrogen uptake)

Whether or not you choose to leave this setting on/off is a personal choice. I have mine set to off. However, as part of my routine, I check/set my mix every single dive.

I had the same question and thank you for a very helpful response

ichigolin:

Why? The "50% O2 for Oxygen and 21% O2 for Nitrogen (79% Nitrogen)" is basically two worst case scenarios (w/in limits).

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Yup - exactly: a 50%O2/79%N2 mix is of course impossible, but it represents the worst case regarding either gas. If left this way on your dive, it means you forgot to set your F02 between tanks.

The nice thing about it is it means you can still dive, your profile will be very safe, the computer doesn't go into violation mode, but you're not likely to get much bottom time. You could set it correctly for a subsequent dive, but things will still be conservative because now the computer thinks you have absorbed more N2 and O2 than you actually have.

I've tried it both on and off, for now I'm leaving it on. I've only forgotten to change it between dives once. That was because the dives were such shallow shore dives that I didn't need to change my HP120 tank in between, and usually it's when I change tanks that I reset the F02 on the Wisdom, so it was not my normal routine and I forgot. In this case it didn't make much difference, because even with the "worst case" numbers kicked in by the default FO2 setting, the dive was so shallow that I was limited by my remaining gas more than N2/O2 absorption.

I think many, if not most, dive computers have a similar setting; and again, some leave it on, some turn it off.

>*< Fritz

How did you reset it?

Xaryo:

How did you reset it?

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Erm... if you're referring to when I said, "usually it's when I change tanks that I reset the F02 on the Wisdom", all I mean by that is setting the FO2 again like you would normally do. Re-Set more than reset I guess.

There's no way I know to reset your N2 and O2 tracking on the computer. I suppose you could yank the batteries out for awhile.

>*< Fritz

no there is a way. At least for the Insight. It is written in the owner manual.

One time, while testing all the buttons combinations, I got the screen shown in the manual regarding the reseting of the computer, but I don't remenber how I got there.

By the way, I discovered something interesting about the Wisdom and the default FO2 setting this week diving in Cozumel. I was typically diving with my first tank Nitrox and my second plain air due to cost (the air tanks were free as part of our package, Nitrox was $10 but worth it for me on the first, deeper dive to reduce overall nitrogen saturation).

So I knew I would have to leave the Wisdom in Nitrox mode and just change the FO2 down to 21% when I went on air, and that if I didn't, the default FO2 of 50% would kick in (because my Default FO2 setting is ON).

The interesting thing, however, is that once I set my FO2 to 21% (i.e. plain air), the Wisdom would keep that even between tanks, and not default back to 50% default FO2 like it would after a typical 32% or 36% nitrox mix.

In other words, even though it's still in Nitrox mode when you set the FO2 to 21%, it acts otherwise like it's in Air mode and does not seem to resort to default FO2 between tanks.

Anyone else noticed this? It does actually make sense.

>*< Fritz

I noticed it. In fact, I read it in the owner manual of the Insight.

All that info was great! Thanks everyone.

Same question, six years later. Just certified Nitrox and have the Wisdom (bought in '06) that has only been set for "air". Putting all that knowledge to the test next week in Florida in preparation for a 10 day live-aboard in Palau in Feb.