A charging scale is a high-precision electronic scale used to weigh refrigerant as it is added to or removed from an HVAC system. Because modern systems use specific refrigerant blends, the charge must be accurate to within a fraction of an ounce to meet efficiency standards. Guessing the charge based on "feel" or "sight" is no longer acceptable in the professional trade. The scale allows the technician to add the exact amount of refrigerant specified on the manufacturer’s data plate, factoring in the length of the line set. It is an essential tool for ensuring a new installation performs exactly as engineered.