There is a procedure in the Aladdin manual. Basically, you have to set zero and span (tank empty, tank full). At empty, the sensor give a 5 digit # that you write down, then you fill the tank and write down that #. You go into Aladdin setup (need a code, its in the manual) and enter the values you have written down. I've got the manual here somewhere, I'll look for it and post it if I can find it.