Peter Guy:(I don't know if I should start this new on the DIR forum or continue it here -- which I shall -- in hopes of getting a "proper" answer.)
PF replied to my question regarding the SPG that it is the only non-redundant piece of equipment the team has. If true (and I believe it is) then, by my understanding of the rule of redundantcy, the SPG is a non-critical device and the redundant information about tank pressure comes from a knowledge of three things, diver's RMV/SAC, time and depth (which is consistent with the training of being able to estimate one's pressure at any time during the dive).
BUT, if the SPG IS a non-critical device, then why would it matter so much that it be of only one kind -- chrome plated brass with glass cover?
I don't believe it is a non-critical device. If there is a leak, knowing SAC/time/depth will not tell you tank pressure.