Calibration is determining the errors in a device relative to a standard, calculating a correction factor, and correcting the errors. Precision weights meet the requirements of one of the four classes. Use Class 1 and Class 2 weights as standards for calibration of analytical balances, in the calibration of lesser class weights, and as counterweights with analytical balances. Use Class 3 and Class 4 weights as working weights and for calibration of general-purpose balances. General-purpose weights are also known as Class F weights. Use these as counter-weights in general-purpose balances and to calibrate scales to commercial tolerances. Most chrome plated, brass, and cast iron weights are general-purpose weights.