Guess the PSI

[Bob DBF]

Personally I would not throw it away.
Just because the bottom end is out.
Just act accordingly.

I still dive SPGs from the '70's that are less accurate than his, at the low end. They are pretty accurate once one isn't at the low end, so they work fine for me.

 

[Waterwulf]

I use analog SPG's on my gear too but only the ones that go to 4K psi. I think they're more accurate than the 5K ones but I still check them against a known gauge.

 

[Bigbella]

Just for kicks, I recently compared one of my 450 bar analogue gauges, at the far lower end, (as close to a 25 bar hash mark that I could determine), with that of a Shearwater Swift transmitter reading; and, surprisingly, the numbers reasonably jibed, to within about 3 bar (about 44 psi) on a nearly empty tank, while setting a regulator’s IP -- not too bad . . .

 

[lowwall]

No, you should never, ever get there. Your dive SHOULD, by the book, be over at 500. But there are emergencies. They do happen. Not being familiar with the limits of your equipment in an emergency only adds to the increased anxiety of the events.

The exact number does not matter in any situation that gets you down to margin of error gas reserves. If you are there, the only thing you need to know is that you need to ascend immediately.

If an emergency is preventing you from ascending such as an entanglement, you need to be dedicated 100% to solving that problem instead of messing with your gauges.

I'm trying to think of other possibilities. Helping another diver that can't ascend? Either go for help or keep working the problem but be mentally prepared for a CESA. Screwed up and have a deco obligation greater than gas remaining?
This might be a time where greater precision would be useful, because you are going to have to make a decision about whether you should follow the computer's ceilings or go straight to 10-15' (3-4m) and suck the tank dry.