posssible tank pressure @ 18 psi, shut-off at 50?

My captive-air bladder tank is supposed to be 40 psi, with the cuton/off at 40/60, according to the manufacturer.

The gauge reads cut on at 50, off at 60, and the tank reads 18 psi (by use of tire gauge).

Is this even possible, or is something not calibrated properly?

We have low water pressure, but no short-cycling, no water coming out of the tank valve, tank appears to have water in it.

Thanks for your help.

When the water pressure is higher than the precharge, both should read the same.

Put 35# of air in the tank and see if it stays.