The measurements are interchangable for my purposes (assuming a SAC rate comes with the tank details) because they both represent the same thing - how much a diver breaths per minute. The difference is essentually one of units (kind of like converting temperatures from F to C).
You can convert from RMV to SAC:
RMV = SAC / tank_service_pressure * tank_volume
Or you can convert from RMV to SAC:
SAC = tank_service_pressure * tank_volume / RMV
That being said, a given number should be associated with the correct term. It could be confusing if you said your SAC is 0.7 because that suggests that you are consuming 0.7 psi/minute when what you mean is 0.7 cf/m.
I think what several of us are saying is that because we can easily convert from one to another, either method of representing the measurement suffices. I think what you're saying is that people should be careful to represent their measurements as eithing being psi/minute or cf/m, and that it's confusing when they use a term which generally refers to one and then use the units that are associated with the other.
The fact that the numbers themselves generally point out which units are being used (cf/m answers are generally in the 0.3 - 1.5 range, and psi/m numbers are generally in the 3 - 50 range (small singles to large doubles)) helps as a rule of thumb but could lead to poor test result interpretation at some point.
What might be best is if we didn't worry about the term SAC, SCR, or RMV, and simply said: my breathing rate is x cf/m or my breathing rate is x psi/m (with tank x).
Andy - I respect that you are being sincere and am working to present you with a sincere explanation.
