That an OOA situation may also ocure due to somekind of malfunction that has nothing to do with gauges. Starting with an O-ring burst, all the way to hoze tear. And I may also add that with new regulators a free-flow may also do it. I made an exsperiment with one of the best regs around, the kind that gives you air so easily. The tank went from full to half full in less than 5 seconds in a shalow dive. Those incidents ARE VERY RARE, but nothing is 100% full-proof.