Here is a better picture showing the gauge past 10 and it is not even hooked up to a cylinder
I will try your method and report.
Actually, that's a 10 kg/cm2 rather than psi, lbs/in2; sorry I missed that originally. No need to try my method if the regulator is not hooked up, just open the needle valve or the regulator valve while its not on the gas cylinder. If it doesn't go down, its more than likely just bad. YOu can replace it or not worry about it. The low, or 'working,' pressure gauge, IIRC, isn't even guaranteed to work on the new units.
Willing to bet, though, its busted. Milwaukee's method to adjust the bubbles/second doesn't rely on the low-side gauge anyway.