2 Questions RE Suunto Dive Manager

[stiebs]

After all, there really is more than just two data points available. It may be true that there are only two cyllinder pressure data points but there are dozens of depth data points which we all know have a significant bearing on air usage.

You can't just create data points. You can only make assumptions. In your graph, you make the assumption that SAC remains constant through out the dive, and you extrapolate a tank pressure graph using that assumption. SDM makes the assumption that tank pressure decreases on a constant gradient between two known sample points, and it extrapolates SAC using that assumption.

Your method is arguably more accurate. But as far as the purpose of the software is concerned, you are working backwards. The SDM software is written to represent actual data which is logged from the computer. What you are attempting to do is recreate that data in lieu of not have a device which can accurately record it.

If Suunto did not offer a range of computers that record real tank pressure data, I would agree with your point of view. But since you are attempting to use a feature which your computer does not support, I disagree with you

 

[John_B]

Would you mind telling me why? I'm just curious because I thought it was a neat idea and that, one day, I'd like to get one. Sure, I don't think it should be used to replace your SPG but for retrospective annalysis of a dive I'm sure the information it provides would be interesting at the least and perhaps even useful.

IMO its a solution in search of a problem. I use a brass & glass SPG and check it regularly, it tells me all I need to know, doesn't rely on wireless electronics, and I'm getting the point where I can estimate what it'll read before checking it. If I know my time, average depth, and start/end pressure I have all I need to calculate my SAC.

Yes, there is a wow factor, but as a newish diver I'd bet there is other gear you could use that is more important than a dive computer pressure transmitter. We're talking some serious jack, here.

Besides, if you did what I do for a living you'd have an innate distrust of computers too.

BTW, Deefstes, your sig mistakes schizophrenia for dissociated identity disorder. Nice poem. Bill Murray in "What About Bob?" right?

Robin Williams in his standup days used to do a shtick something like:

"I'm a schizophrenic!", "No I'm not!", "Yes I am!", "Shut up, the both of you!"...

 

[Deefstes]

If Suunto did not offer a range of computers that record real tank pressure data, I would agree with your point of view. But since you are attempting to use a feature which your computer does not support, I disagree with you

OK, I concede. You're right, if I want that sort of extrapolations I should do them myself and not expect the software which was designed to deal with air integrated computers to do it.

IMO its a solution in search of a problem. I use a brass & glass SPG and check it regularly, it tells me all I need to know, doesn't rely on wireless electronics...
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as a newish diver I'd bet there is other gear you could use that is more important than a dive computer pressure transmitter.

Good point, thanks for the input. But seeing as you've taken the bait, I'm going to keep throwing noob questions at you for a bit - milk it while I can.

What makes a brass and glass SPG so special? I've seen them around and it's usually on the realy experienced divers' gear config that I see them. I figured it could be for one of two reasons, either the guy has been diving for so long that he bought his SPG before the new rubberised ones were available or because he is so experienced that he knows something that the others don't and actually prefer the brass and glass gauge.

Also the only brass and glass gauges I've seen were only for cyllinder pressure. So what do you use then for depth measurement?

BTW, Deefstes, your sig mistakes schizophrenia for dissociated identity disorder. Nice poem. Bill Murray in "What About Bob?" right?

I think the quote has been used by numerous people, amongst others Bill Murray in "What About Bob?" and Billy Connoly but from what I understand it is attributed to Oscar Levant.

Another one I like is Henny Youngman's response of "...What, you too? Then that makes four of us!"

 

[stiebs]

What makes a brass and glass SPG so special? I've seen them around and it's usually on the realy experienced divers' gear config that I see them. I figured it could be for one of two reasons, either the guy has been diving for so long that he bought his SPG before the new rubberised ones were available or because he is so experienced that he knows something that the others don't and actually prefer the brass and glass gauge.
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Also the only brass and glass gauges I've seen were only for cyllinder pressure. So what do you use then for depth measurement?

A couple of reasons, some more applicable than others. A rubber boot around the SPG can trap salt sediment and cause crystals to form, assisting corrosion and possibly jamming the connection so the guage can't rotate on the hose. The rubber boot also increases bulk without adding much, if any function.

A combo guage with SPG, depth guage (or computer) and compass is a massive and heavy piece of equipment that houses all of your dive data, and it is (arguably) inconvenient to keep an eye on. Move your compass and computer to wrist mount, and most of your dive data is in front of you all the time. Just your SPG is a short reach away. You have a Mosquito, why do you need a depth guage?

Think of an ascent. With a combo guage you're holding the guage monitoring your depth/saftey stop with your left hand. Then you need to make a buoyancy adjustment. Either drop your guage for the moment, or pass it across to your right hand to make buoyancy change with your left. Or reach across to your inflator hose with your right.

Now your computer is on your wrist or forearm (right arm preferred) and you just have a brass SPG. You've turned or called the dive and on your ascent/safety stop. You need to know depth and time, but there's no real reason to monitor air pressure. Just keep your right arm out in front to watch your computer, left arm is free to control buoyancy, and SPG is clipped out of the way.

 

[John_B]

Just to chime in here, I agree with everything Mark just said. You have a Mosquito, that will work fine for at least the near future and probably a lot longer. You can spend more, but why. Use it as a computer if you want or that's what you are comfortable with, just don't turn your brain off and let it do all your thinking for you.

FWIW since you asked, I currently use a dive computer in gauge mode on my right arm (and compass on the left arm), I'm going to try a Sensus Ultra specifically for dive logging so the logging function of the dive computer or bottom timer becomes less of an issue. For me, its part of a system that works very well.

 

[Geezer]

One nice thing about the Sensus is that you can see a graphical representation of your dive on a Palm OS PDA right after the dive, without having to haul a laptop computer around.

 

[LowVizWiz]

Deefstes:

One thing I see you forgot to enter to get your sac from SDM is the working pressure of your cylinder.
Here are 2 graphics of the same dive with different numbers and they give 2 different results.
You actually omitted this info yet SDM gave you a number. Mine crashes when I do that!

This is 3440 working presure which was the actual working pressure...

Here's 3000 working pressure:

Also, this is a Cobra (AI computer) and the air consumption graph is closer to a straight line than your graph...

 

[LowVizWiz]

Wow those are big... I needed a different post to continue =)

... Even though the working pressure is different and the SAC# is different my consumption # is the same 26.4 psi/min which is what I really need for planning.

 

[stiebs]

Deefstes:
One thing I see you forgot to enter to get your sac from SDM is the working pressure of your cylinder.
Here are 2 graphics of the same dive with different numbers and they give 2 different results.
You actually omitted this info yet SDM gave you a number. Mine crashes when I do that!

Aah yes, but LowViz you omitted to notice one piece of vital information. Deef is using metric cylinder capacity, not imperial. A 10L tank a 10L tank regardless of working pressure. Working pressure is only required when specifying capacity in cu.ft.

An 80cu.ft tank when filled to its working pressure will hold the equivalent of 80 cubic feet of air (gas) at 1 atm.

However a 10L tank will hold 10L of water. Its total compressed air (gas) capacity is simply the 1atm volume (10L) X pressure (eg, 210bar). Gives 2100L of gas.

Deef's question is why does SDM show only 1980L instead of 2100L. The only thing I can think of is an adjustment based on ambient temperature.

 

[LowVizWiz]

Working pressure is only required when specifying capacity in cu.ft.

Did not know that... thank you for the clarification! I have no idea about the metric system.