Diver0001:
The DIR style, which to the best of my knowledge is where the 6 inch hose thing came from, has a different kind of context. Think about diving in cramped space with 2 or more stage bottles all slung on teh same side. In that context you might not be able to lift the stage bottle up to see what the spg says. Therefore, at least in that context, it makes your life easier to have a larger gauge prominently mounted......
Actually, that's not why DIR divers like the large face gauge. In fact, the large face gauge thing is not really peculiar to DIR at all - it mostly comes from cave diving.
In cave diving we often utilize stage bottles, which are used to extend our penetration distance into the system beyond what we might be able to do on doubles alone. Stage bottles are considered "managed gas", similar to what's in your doubles - this means that they are breathed and monitored throughout a portion of the dive, according to some sort of overall gas management plan ("thirds", "half plus 200", or something similar). To do this safely, we need to be able to accurately determine cylinder pressure to the nearest 100 PSI.
Cave divers also frequently use a decompression gas to accelerate their off-gassing at the end of the dive. For deco gas, it's usually sufficient to know at the start of a dive that the tank has enough gas in it for the expected deco obligation. In that situation, a separate pressure checker (used at the surface), or a small button gauge would be sufficient to check the contents of the cylinder prior to entering the water.
So for managed gases, we tend to prefer larger gauge faces that are easier to read accurately. For "unmanaged" gases (such as deco gases), it's not strictly necessary to have a large gauge face, since you really only need to check things once at the beginning of a dive. It certainly does not hurt anything to have one, though.
HOWEVER, from the standpoint of regulator rigging, it's much easier if all the regs are configured the same. Cave divers don't typically distinguish between regs that go on stage bottles and regs that go on deco bottles - they're all interchangeable in terms of how they are set up. Since we prefer to rig them all the same way for the purposes of standardization, then it makes the most sense to use the larger gauge faces on everything. That way they can be easily swapped out if a failure occurs (even underwater if necessary).
And of course since a lot of the DIR philosophy is adapted from cave diving, we tend to carry that "context" over into what we do in our other types of diving as well.
Diver0001:
and because it's DIR they want everyone to always do it the same way, even if it's effectively just a pony bottle.
Just a slight clarification - we want "everyone
on our DIR team to always do it the same way". Standardization of gear configuration is a key component of DIR diving, for a lot of the same reasons that I stated above (interchangeability of gear, familiarity with common procedures, etc).
However, we have no control (or even a "right" of control) over what you choose to do on
your team - that is between you and your teammates.
