I don't think anybody calibrates these gas tank senders. They should be checked for a certain resistance at 10 different positions to make sure they are accurate. One of the problems is the winding of the wire resistor. The wire inside a factory original is not linear. They wind the wire closer together at one end to match the rate of drop of the float. This keeps the gauge reading to match the shape of the tank and float arm angle. The last sender that I took apart that was a repro was not made this way, the resistance wire was wound evenly down the whole length.