It's not top of the line, but you can get a liquid filled, 0-30 psi gauge for around $20 here:

http://www.mcmaster.com/#liquid-filled-pressure-gauges/=nu7vvx


"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.