Just buy a pressure/vacuum gauge. They're cheap, and they have a bunch of uses. No shop should be without one.

https://www.amazon.com/8milelake-Vacuum-Tester-Carburetor-Pressure/dp/B01GHD0NAK

Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!