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-based 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; no need to wear glasses when reading measurements. 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 units and images may occur.