Usage: This refractometer measures the ethylene glycol and propylene glycol concentration for frost protection in vehicles, solar installations, heat pumps, cooling systems, heating systems, and other machinery or water systems. Measurement Range: Ethanediol (ethylene glycol): 0 to -50°C; Propanediol (propylene glycol): 0 to -50°C; Windshield cleaning fluid - ethanol + water: 0°C to -40°C; Propylene glycol + water (SRF1): 0°C to -40°C; AdBlue: urea concentration 30% - 35%; Acid battery: 1.10 to 1.40 kg/L. Precision Measurement: Features an optical system with 4-8x magnification and stepless manual focus, suitable for all users, including those with nearsightedness or farsightedness. Reading can be taken without wearing glasses. Calibration: Zero calibration using distilled water at 20°C with automatic temperature compensation. Note: Due to manual measurement and display differences, slight variations between individual products and images may occur.