Designed to test the concentration of salt in water and salt solution, ideal for aquarium, marine monitoring and quality control in research and clinical Laboratories Measurement range: salinity 0- 100‰; (0-10% Salt Content), Specific Gravity 1,000-1,070 SG,(Salinity +/-1‰; - Specific Gravity +/-0.001 SG) Easy to use. Place 2, 3 drops of sample on the main prism, close the plate and look through the window at the reading; CALIBRATION: zero calibration with water at 20°C, automatic temperature compensation between 10°C and 30°C (ATC) Sharp precision measurement dividing line (blue- white), easy to read (daylight visible), adjustable eyepiece for focus adjustment Calibration: zero calibration with distilled water at 20°C, automatic temperature compensation between 10°C and 30°C (ATC).