Pressure gauge help

[Bob3]

"All of the above" comments are good, there's a whole chain involved starting from the tank valve going all the way to the tiny pinhole on the gauge stem. Mischief could be lurking in any number of the items/places between.
I start at the tank & work my way out, checking & eliminating things on the way.
If you have 2 HP ports & an extra gauge that helps.
Be aware that more air volume is needed at depth, so it may not be able to duplicate the symptom topside.

 

[do it easy]

It's not worth dying over a lousy pressure gauge.

I wouldn't throw the guage away, just yet. Have the reg looked at to make sure it's a reg problem. After fixing the reg (or not), then you can decide if the gauge is truly bad.

Good call.