I'm not sure about 'calibration', the tricky bit is setting the orientation of the float arm and angle of the float so it sits in the slope at bottom part of the tank. Once you've done that you can adjust the float arm length (and pivot height, if that type of sender), so there's correct travel from bottom to top. If you do it in situ with liquid then you end up chasing your tail - you get the bottom set, then the top is out, or you hit the baffle etc. Doing this in a mock up where you can see things is a 5 minute job. A lot of the older installs just had the travel set at the mid point height of the tank with the float arm parallel to the long side of the tank and left it at that. As a quick improvement, and starting point for trial and error, you can bend the float arm to angle it forward so the float almost touches the front of the tank, tweek the angle of the float on the arm so it's the same as the slope on the tank and increase the travel for the height at that point. The Caerbont and some of the universals need soldering once set and cut making adjust after more of a pain