Ok guys, here's one for you to ponder....

Why do you have an oxygen pressure gauge on a hose on a CCR?

I can see the point to a diluent gauge that's accessible during the dive, because you might do mask clears, diluent flushes, etc.

But why an O2 gauge you can read? Your metabolic consumption is a relatively known figure, right? You don't go in without enough, right? So..... why?

See, here's why I'm asking. The hose contains quite a bit of gas, and is where the problems with fethering a stuck solenoid come from. Use a button gauge, you can still read it before you dive, but in the water, you can't see it. HOWEVER, you lose all that gas space at tank pressure, which means that feathering a valve becomes a very viable option.

All the rigs I see have gauges for each tank "front and center" - but is it really all that useful? More to the point - is it necessary?