Usage: This refractometer measures the ethylene glycol and propylene glycol concentration for frost protection in your car, solar installation, heat pumps, freezing point detection, heating systems, or other machinery and water installations. 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 the eyepiece group providing 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 products and photos may occur.