I just bought a Serfas FP-200 floor pump and I tested it out on my mountain bike just to see how accurate the pressure gage on it was. I pumped the tire up to 40 psi (according to the pump) and check the pressure with 3 different tire gauges. All three gauges read 45 psi. I wanted to use the pump on my road bike but I'm a little worried it will not be as accurate as I want. Should I just return the pump, buy a cheaper one, get a presta pressure gauge, and call it a day? Or is there a way to adjust the pressure reading on the gauge itself?

Thanks