Usage: This refractometer allows you to determine the ethylene glycol and propylene glycol concentration for frost protection in your car, solar installation, heat pumps, cooling systems, heating systems, or other machinery and water systems. Measurement Range: Ethanediol (ethylene glycol): 0 to -50C; Propanediol (propylene glycol): 0 to -50C; Windshield cleaning fluid - ethanol + water: 0C to -40C; Propylene glycol + water (SRF1): 0C to -40C; AdBlue: urea concentration 30% - 35%; Acid battery: 1.10 to 1.40 kg/L. Precision Measurement: Features an optical system with the eyepiece providing 4-8x magnification and stepless manual focus. Suitable for all users, including those with nearsightedness or farsightedness; it is recommended not to wear glasses when reading the measurement. Calibration: Zero calibration using distilled water at 20C with automatic temperature compensation. Note: Due to manual measurement and screen display differences, slight variations between individual products and images may occur.