See also commit acb38c9e00f2. pSCR is with respect to cylinder planning very
similar to OC planning. Obviously, the SAC is much (max. 8x for counterlung
ration 1:10) lower, but multiple gasses are common (in all but recreational
pSCR diving).
Changed the wording to reflect this.
Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>