Hey bikework I hope you answer this question. I just bought a planet bike dial gauge from Jenson. It says it works on a presta or shraeder. The valve seems to fit a presta o.k., but I know the reading can't be right cause I just got the bike back from the LBS and he said he put 90psi in the tire. The gauge only registers 50psi. I'm using it like a car tire gauge. Is this correct? Also I don't know how to convert for shraeder use. The screw cap comes off and then it fits the shraeder, but no reading. Can this brand new gauge be defective or am I just an idiot?