After the instruments have been installed and are working properly, the floats need to be calibrated. As the tank is filled using the turbine meter, the data logger counts gallons and records float voltage output as each gallon enters the tank. The resulting data logger file (fill file) for each float contains two data columns: the first lists gallons in the tank and the second lists the corresponding output voltage. Each float is calibrated three times and the data from each calibration is graphed for comparison. The most representative fill files are selected and used to convert voltage output to volume for the rest of the test. If a float is replaced or relocated, calibrate it again.