A common mistake is the meter is not adjusted to the proper setting for what you are measuring. If you are checking the DC resistance of a pickup, make sure that you have it set on the proper setting. Make sure the leads are inserted into the proper socket. Make sure you have no breaks in the connections or plugs on your leads. Make sure the leads are properly plugged inserted tightly into the socket. Check the battery on occasion. I often check the calibration of my meter by using a known value resister or power source and make sure the reading on the meter is the same. If the calibration is off, then the meter should be sent in for service.