Geo Setup Question

[Vlane]

I have my first dive in over a year this saturday and my first dive with my geo. I've been going through the setup but have a question about setting up a dive in NORM mode

During the SetF setup FO2 is set default as air, if i choose select and go up from there it defaults to 21% FO2 and if i go past 50% mix it goes back to air. At the next screen it has an option to turn default of FO2 at 50% on or off.

I'm just going to be using standard air for this dive so i'm assuming i leave the first setting on air. Secondly, what do i do about the default FO2 at 50%? I currently do not have my nitrox certification so should i turn this default setting off?

[reactive]

Yes, just leave it on air. The second setting (defalut 50%) will automatically set your FO2 to 50% if you set your computer to anything other than air, and then make another dive without going back in to set the blend you are using.

Example: Dive 1 you set your computer to 32% and make a dive. Then you go for dive number 2 and you forget to set the mix of O2 in your tank. The computer will defalut to 50% (assuming 50% O2) and give you bottom times accordingly.

If you aren't using nitrox at all, just leave the FO2 setting to Air and and don't worry about the other setting. It will not default you to 50% if you are using "Air" as the setting.

[Vlane]

Thanks for the clarification. The people who write these manual aren't always very clear in explaining things haha.

[navyhmc]

Another note on the 50% default. If you turn it off, the PO2 setting (O2%) will stay at the last selection you made-if using nitrox. A nice feature if you are using the same O2% on every dive, but can be dangerous in your PO2 changes from dive to dive.

[ScubaToys Larry]

Just a slight clarification on this explanation... That default 50% will sorta' set the mix to 50% if you don't set it for the second dive - but it will also set it for 21% at the same time.

What?!?!

Ok... Here's the deal. Your dive computer has a pretty good gig. Doesn't have a day job, doesn't have to pay taxes, all it has to do is go diving with you now and then. (Where do I sign up!) But it does have a few issues it has to deal with. His real job is to keep you safe when diving. And when diving with Nitrox, there are two real issues we are looking at:

1) bottom time
2) Oxygen Toxicity

So you do the first dive and set it for 32% for a nitrox dive. Then you come out, wait an hour or so, and hop back in... but forget to tell the computer what you are on now. Are you on another 32?? Or air for this one? Or a 36%? What's a poor computer to do!

So it assumes you are on air for your bottom times. If you are on air, but it thought you were on a nitrox mix, it would give you longer times, and you might bend up like a pretzel... so it will assume you are on air.

But with Nitrox, we have that pesky MOD (maximum operating depth) of a gas - the depth at which the increased O2 in the mix can mess with your nervous system - sending you into convulsions. (And actually the convulsions don't kill you... it's that spitting out a reg at 140 feet that proves to be unhealthy... but I digress)

So to make sure you don't go too deep, the computer sets your MOD as if you were using a 50% mix and if you go past about 60 feet or so, it starts beeping, flashing, shouting at you... But for the bottom time, it's assuming 21% good ole' fashioned air.

So when would you turn this feature on or off?

Excellent question!

With it set off, it assumes that your next dive is using the exact same mix as your previous dive. So if on a live aboard where they have very consistent mixes of say 32% dive after dive - you might want to turn it off so you don't have to set it each time. But if doing a series of shore dives and getting tanks from a different place each time, you would probably want it turned on - making you set the FO2 for each dive.

I'd say, leave it on, and then get in the habit of setting the computer before every dive no matter what.

But for your air dives... here's what you do. Don't play with the buttons. Put it on your wrist... jump in the water, don't let the big number hit zero. That's it!

Have fun! (now that you are thoroughly confused!)

[I Like 2 Dive]

Originally Posted by Vlane

I have my first dive in over a year this saturday and my first dive with my geo. I've been going through the setup but have a question about setting up a dive in NORM mode

During the SetF setup FO2 is set default as air, if i choose select and go up from there it defaults to 21% FO2 and if i go past 50% mix it goes back to air. At the next screen it has an option to turn default of FO2 at 50% on or off.

I'm just going to be using standard air for this dive so I'm assuming i leave the first setting on air. Secondly, what do i do about the default FO2 at 50%? I currently do not have my nitrox certification so should i turn this default setting off?

Is your Geo the newer model or older one? I just bought the newer model myself, but haven't gotten it wet yet. I will in May. I'm like you, not nitrox certified, so I just use air. Keep me posted how you like your Geo. I'm looking forward to hearing how it performed for you.

[reactive]

Originally Posted by I Like 2 Dive

Is your Geo the newer model or older one? I just bought the newer model myself, but haven't gotten it wet yet. I will in May. I'm like you, not nitrox certified, so I just use air. Keep me posted how you like your Geo. I'm looking forward to hearing how it performed for you.

As far as I know, the software and display on the older and newer GEO's are the same. The new one just has improved looks. At least that's what I was told when I bought the older model over the newer model from ST.

[reactive]

Originally Posted by ScubaToys Larry

Just a slight clarification on this explanation... That default 50% will sorta' set the mix to 50% if you don't set it for the second dive - but it will also set it for 21% at the same time.

What?!?!

Ok... Here's the deal. Your dive computer has a pretty good gig. Doesn't have a day job, doesn't have to pay taxes, all it has to do is go diving with you now and then. (Where do I sign up!) But it does have a few issues it has to deal with. His real job is to keep you safe when diving. And when diving with Nitrox, there are two real issues we are looking at:

1) bottom time
2) Oxygen Toxicity

So you do the first dive and set it for 32% for a nitrox dive. Then you come out, wait an hour or so, and hop back in... but forget to tell the computer what you are on now. Are you on another 32?? Or air for this one? Or a 36%? What's a poor computer to do!

So it assumes you are on air for your bottom times. If you are on air, but it thought you were on a nitrox mix, it would give you longer times, and you might bend up like a pretzel... so it will assume you are on air.

But with Nitrox, we have that pesky MOD (maximum operating depth) of a gas - the depth at which the increased O2 in the mix can mess with your nervous system - sending you into convulsions. (And actually the convulsions don't kill you... it's that spitting out a reg at 140 feet that proves to be unhealthy... but I digress)

So to make sure you don't go too deep, the computer sets your MOD as if you were using a 50% mix and if you go past about 60 feet or so, it starts beeping, flashing, shouting at you... But for the bottom time, it's assuming 21% good ole' fashioned air.

So when would you turn this feature on or off?

Excellent question!

With it set off, it assumes that your next dive is using the exact same mix as your previous dive. So if on a live aboard where they have very consistent mixes of say 32% dive after dive - you might want to turn it off so you don't have to set it each time. But if doing a series of shore dives and getting tanks from a different place each time, you would probably want it turned on - making you set the FO2 for each dive.

I'd say, leave it on, and then get in the habit of setting the computer before every dive no matter what.

But for your air dives... here's what you do. Don't play with the buttons. Put it on your wrist... jump in the water, don't let the big number hit zero. That's it!

Have fun! (now that you are thoroughly confused!)

Good to know Larry. Consider me schooled.

[Vlane]

Wow larry, great explanation that helps a lot. Hoping to move up to nitrox one of these days but need to get a lot more dives under my belt first .

@I like 2 dive
I'll try and remember to let you know how it goes on saturday. If you don't hear back from me feel free to PM me and ask some questions though.

[Miked]

Good explanation Larry.

In effect, the computer is acting as if you have a mix that is 50% O2 AND 78% Nitrogen. An impossible mix to have, but it does keep the diver in a safer situation (given that the computer doesn't "know" the mix that is being used.