This may be part of the problem. SRMV is redundant, since RMV is defined at 1 atm. As tempting as it is, we don't get to make up our own definitions, that path leads to confusion. Regardless of common practice by divers (myself included), if you go back to primary sources (like the Navy dive manual and the NOAA dive manual), RMV is volume/minute, SAC is pressure/minute; the latter has SURFACE in its name, so there should be no confusion, but of course there is, It doesn't help that PADI says SAC can be in pressure or volume, but at least they say RMV is always volume (I guess it helps to have VOLUME in the name!) It helps even less that TDI defines SAC as volume/minute, and asserts it is a constant, along with claiming that RMV is your actual breathing rate at depth, while working.
Conclusion? You need to know it, for you, whatever you want to call it. You'll probably calculate it as pressure/minute at depth, and convert that back to pressure/minute at the surface, so you have a single number to remember that you can use.at all depths....with that cylinder. You ought to go further and convert YOUR number to volume/minute, at the surface, because now you can use it for all cylinders.
