SAC & RMV Differences

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acreichman
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SAC & RMV Differences

Post by acreichman » Tue Dec 03, 2019 1:37 pm

I know some similar questions have been asked in these forums but I have a couple of questions I haven't been able to find an answer to.

1. Is the only difference between SAC and RMV (besides the units) that SAC rate is at the surface and RMV is at depth? If not, what are the differences between SAC & RMV?

2. In MacDive, the units for SAC rate are psi/min and RMV is ft^3/min. When I learned SAC rate, it was in ft^3/min. Is there a way to change the unit into ft^3/min?

3. I don't always use the same size tank so I need a measure of volume used per minute at the surface to plan my dives. Based on my understanding of SAC & RMV above, I don't think that particular metric is available in MacDive. Is there something I'm missing here? How do the rest of you plan dives without a measure of volume used at the surface?

Thanks very much for your help.

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nick
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Re: SAC & RMV Differences

Post by nick » Tue Dec 03, 2019 1:40 pm

1. Is the only difference between SAC and RMV (besides the units) that SAC rate is at the surface and RMV is at depth? If not, what are the differences between SAC & RMV?
No. Both factor depth, but RMV also factors the tank.
2. In MacDive, the units for SAC rate are psi/min and RMV is ft^3/min. When I learned SAC rate, it was in ft^3/min. Is there a way to change the unit into ft^3/min?
No, the units reflect what they have calculated.
3. I don't always use the same size tank so I need a measure of volume used per minute at the surface to plan my dives. Based on my understanding of SAC & RMV above, I don't think that particular metric is available in MacDive. Is there something I'm missing here? How do the rest of you plan dives without a measure of volume used at the surface?
RMV factors the tank size/volume.

acreichman
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Joined: Fri Feb 08, 2019 1:37 am
Dive Computer: Suunto Eon Core

Re: SAC & RMV Differences

Post by acreichman » Thu Dec 05, 2019 1:47 am

Sorry, I'm still a little confused. If I use 500psi over 10 minutes at 2atm, my SAC rate should 50/2 or 25psi/(min*atm) but I can't use that number to compare different dives using different tanks. When calculating RMV, is my 50 psi/min then divided by 2atm before using tank info to convert to cubic feet? When I use different tanks at a variety of depths, which one should I be using to see if my air consumption is improving over time?

Thanks again for responding so quickly.

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nick
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Re: SAC & RMV Differences

Post by nick » Thu Dec 05, 2019 1:54 am

The RMV.

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