The models have only one unit system: °C. With the indication of the percentage we may know the freezing point of either ethylene glycol or propylene glycol based cooling systems. And they can also be used to test the concentration of ethylene glycol or propylene glycol in antifreeze liquids. Also, it is added a scale for measuring the the freezing point of windshield cleaning fluid. The RHA-503ATC has Automatic Temperature Compensation System. Measuring Range: Ethylene Glycol:-50°C-0°C Propylene Glycol:-50°C-0°C Cleaning Fluids:-40°C-0°C Battery Fluids:1.100-1.400sg Resolution Factor: 5°C,5°C,5°C,0.01sg (ATC) Temperature Compensation Range:10°C--30°C