Looking for a nice Air Integrated, liberal decom(or able to change liberal/conservativeness) computer. Open to literally anything.

[Belzelbub]

What’s RMV?

There’s a long thread on SAC vs. RMV somewhere on here. There is some debate, but the generally accepted answer is:

SAC is Surface Air Consumption, and is measured in PSI/min.
RMV is Residual Minute Volume, and is measured in cu ft/min.

Both are a measure of consumption at 1 atmosphere. With SAC, you can’t transfer to a larger or smaller tank as the rate you consume PSI will change. With RMV, the rate is in actual volume consumed at the surface. With either SAC or RMV you would need to convert for depth to figure out how long a given amount of gas will last.

 

[ATJ]

SAC is Surface Air Consumption, and is measured in PSI/min.
RMV is Residual Minute Volume, and is measured in cu ft/min.

Or for the rest of the world

SAC is Surface Air Consumption, and is measured in bar/min.
RMV is Residual Minute Volume, and is measured in L/min.

 

[Blackcrusader]

So how will the perdix know my average air consumption for those calculations? Does it learn it over time?

In diving log and other computer logs you are able to enter the tank size, starting pressure and ending pressure and the log can calculate that dives sac rate. So you need to keep a record of this manually. You will also get your average depth for each dive as well. Others have answered as well. I have this dive saved in my Shearwater Desktop and also in Divinglog.com To average all your dives you would need to count up all the dives.

In Shearwater Cloud look to the right under Gases. You can see I entered my tank size and starting pressure and ending pressure.
Average 1.72 bar/min The tank was an AL80 210 bar start is about 3045 psi and end 50 bar 725 psi for a 93 minute dive.

In divinglog you can see the same time but log shows air at end of dive and also displays the RMV of 7.86 liters /min

Normally my dives are less than 8l/min but on the high end of my last 250 dives the highest was 9.85l/min on a dive where I spent the half of the dive swimming against a current. Diving conditions your diving techniques your breathing management all affect your use of gas as does your depth on the dives.

 

[Blackcrusader]

What’s RMV?

read this thread.

Average Gas Consumption

@Dan Both SAC and RMV are adjusted for surface consumption using average depth/atm of your dive, right? Take a look at the calculations Average Gas Consumption

scubaboard.com

 

[ATJ]

I have this dive saved in my Shearwater Desktop

That looks more like Shearwater Cloud which is a separate and different app from Shearwater Desktop.

 

[Blackcrusader]

That looks more like Shearwater Cloud which is a separate and different app from Shearwater Desktop.

Yes I have both thanks for the correction if I erred. I like using divinglog to get the liters/min record.

Cloud update now shows pressure change rather than average sac bar/min

 

[ATJ]

Average 1.72 bar/min The tank was an AL80 210 bar start is about 3045 psi and end 50 bar 725 psi for a 93 minute dive.

In divinglog you can see the same time but log shows air at end of dive and also displays the RMV of 7.86 liters /min

There's something weird about those numbers. Isn't an AL80 11.1L? That would make the RMV 19.092 (1.72*11.1) (not allowing for the non-linear compression of air).

 

[Blackcrusader]

There's something weird about those numbers. Isn't an AL80 11.1L? That would make the RMV 19.092 (1.72*11.1) (not allowing for the non-linear compression of air).

I am just posting what the logs show. Just means I have decent gas consumption on dives.

 

[ATJ]

Average 1.72 bar/min The tank was an AL80 210 bar start is about 3045 psi and end 50 bar 725 psi for a 93 minute dive.

I worked it out - at least partially.

The SAC was not 1.72 bar/min but the actual consumption (i.e. not taking depth into account).

(210-50)/93 = 1.72.

To get SAC you have to divide by (average depth (in metres)+10)/10.

It appears your average depth was 14.22m so your SAC was actually

1.72/((14.22+10)/10) = 0.70

 

[Blackcrusader]

I worked it out - at least partially.
The SAC was not 1.72 bar/min but the actual consumption (i.e. not taking depth into account).
(210-50)/93 = 1.72.
To get SAC you have to divide by (average depth (in metres)+10)/10.
It appears your average depth was 14.22m so your SAC was actually
1.72/(14.22+10)/10 = 0.70

Thanks for that. Divinglog lists average depth as being 14.22m but Cloud does not it seems.
I assumed Shearwater cloud used the actual consumption 1.72 bar/min for the dive. 210 - 50 is 160 bar used.
160 divided by 93 mins is 1.72.

Knowing the size of the tank one can work out how many liters the tank holds at 210 bar and how many liters were used so you can do the math with that to work out RMV. Can use that to plan other dives. If was was planning to do say a square profile dive 20m for 65 minutes on 32% I would need an AL80 if my sac rate was 10l/min using around 1920 liters of gas. So that NDL dive could be planned on an AL 80 210 bar which holds over 2300 liters of gas. Of course if I planned that but actually used more gas say due to swimming against a strong current I have no deco obligation so can safely ascend do a safety stop and end the dive. If I was at my good sac rate of 8l/min I only need around 1550 liters of gas, easily done and even if I did a light deco dive to 75 minutes I would be able to complete my added deco time of 7 minutes and require 1805 liters of gas. Of course people will say don't plan that without having an additional tank rather than a single tank. I could use an AL100 which would be better.

I do not gas plan multilevel NDL recreational dives. I do not know anyone who does actually.

It's good to be able to view my dives in two different systems as they offer different information.
I like using diving log to see what my gas status was on any point of a dive. ScubaBadger32: will be wanting to learn all this tank size and pressure and how much gas is in them so can calculate gas tank size required for a dive.