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Travman
03-10-2009, 16:51
I have a Mares Airlab which calculates my SCR on the fly and displays an an average for the dive in the log book at the end of the dive. It gives me the figure in litres per minute (I use metric) as a surface consumption rate. I have found this useful to see how different things change my breathing rate as well as how my breathing rate changes with experience.
I recently did a deep diving course and everyone groaned when we were asked to figure out our SCR, but thanks to my computer I already knew what mine was.
My friends that I dive with are all very jealous of this small feature as some of them have top-end computers that cost double the Airlab and they all want to borrow it for a dive or two to check their SCR. The only downside is you need to programme in the tanks volume before the dive.
Are there any other computers around other than the Mares Airlab and Nemo Air that give the SCR in an actual figure, not a bar graph?

clayton
03-10-2009, 17:28
my sherwood wisdom 2 does it in the download page,just type in the tank size.

SynCitizen
03-10-2009, 17:52
Cobra2 does as well when downloaded.

CompuDude
03-10-2009, 18:22
Most AI computers can calculate SCR when downloaded, but I can't recall seeing any that did it on the dive computer itself. It's not the dive computer that calculates it, most of the time, it's the desktop software. As noted, you can't do it without entering tank capacity, and I have yet to lay eyes on a computer where you do that. Interesting feature.

bubbletrubble
03-10-2009, 20:10
@Travman: Your lazy buddies know that SCR (or RMV) can be calculated very easily with just a few variables, right? Note that this "manual" method will only calculate an SCR for an entire dive...it won't give you an instantaneous SCR.
Since most dive computers will calculate the average depth for the dive, the only other pieces of info you need to know are the following non-computer items: tank capacity, tank service pressure, duration of dive, beginning tank pressure, and ending tank pressure.
(tank capacity cuft/tank service pressure psi)(start pressure psi - end pressure psi)/(avg depth ft/33+1)/(dive duration minutes) = RMV in cuft/min
[this particular equation will only work for imperial units -- it has to be tweaked a little for metric]
An air-integrated computer is nice and all, but we simply can't have your buddies "stealing" your dive computer like that. :D

Flatliner
03-10-2009, 22:43
The cobra I used to dive did it. Now I do it manually after the dive (moved to non air integrated wrist comp and gave the cobra to my son)

Travman
03-10-2009, 23:29
Bubbletrubble - yes I have told them how to figure it out a few times, but us Gen Y people want computers to do all the work for us :)

navyhmc
03-11-2009, 00:19
I have a Geo and after I down load the dive, I can enter starting PSI, ending PSI and tank size and it will compute RMV for me as well. Usually I have it done before I download the computer. The computer is good at this as it will calculate you average depth even if you do a non-typical profile and calculate you RMV off of that.

This feature is very nice when I'm solo diving. In my planning, I've made a fairly accurate gas plan off of my SAC, the planned depth, the dive, the planned length of the dive and factors such as wet suit or not, cold water, etc. Using both, confirms my plan or gives me some data to modify it next time.

Heavy D
03-11-2009, 15:07
I know that the Uwatec/Scubapro does it on the fly when figuring your dive time remaining and such but I'm not sure if it displays it. I'll have to ask my buddy who has the computer.

SAC rate is really easy to calculate manually though so I don't see whay they are groaning so much.

cummings66
03-11-2009, 15:27
The trouble with a computer doing it is that you don't know for sure how accurate it is. I'm an advocate of going to the platform for 5 minutes and testing it 3 ways, so it takes 15 minutes to do.

Go down there and rest, don't move for 5 minutes. That's your deco SCR, now do some light finning like you are diving, that's your normal SCR, now fin as hard as you can, try to move that platform, be careful not to over breathe the reg because this time depending on reg you'll find that maybe you suck so much air that you can't get enough. This is your working SCR. All 3 are useful to know, and since it's at one depth only you have a postive idea of what it is. There is no averaging it as a computer does because you're at one depth the whole time.

But yes, I've seen computers do it and I sort of think it'd be a neat feature to test some theories on quickly.

CompuDude
03-11-2009, 16:32
The trouble with a computer doing it is that you don't know for sure how accurate it is. I'm an advocate of going to the platform for 5 minutes and testing it 3 ways, so it takes 15 minutes to do.

Go down there and rest, don't move for 5 minutes. That's your deco SCR, now do some light finning like you are diving, that's your normal SCR, now fin as hard as you can, try to move that platform, be careful not to over breathe the reg because this time depending on reg you'll find that maybe you suck so much air that you can't get enough. This is your working SCR. All 3 are useful to know, and since it's at one depth only you have a postive idea of what it is. There is no averaging it as a computer does because you're at one depth the whole time.

But yes, I've seen computers do it and I sort of think it'd be a neat feature to test some theories on quickly.

So you trust your computer to accurately monitor depth and time, but not it's ability to do basic math to determine average depth and air consumption? That makes no sense to me.

I agree your method is simple, but if you have an AI computer it's quite nice to precisely track your SCR as it changes over time... you can start to see trends quite clearly that way.

I don't know that I would trust a manual SCR calc that I took 6 months ago to accurately predict my SCR on tomorrow's dive, unless I've established a pattern over a very long period of time. Not faulting the calculation method, just the timeliness of the data if you don't want to repeat your 15 minute test on a regular basis. (No choice if you don't have AI, but if you do, that's a lot of extra diving time you don't have to waste on SCR tests!)