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 compensation for temperature between 10°C and 30°C (ATC). Please note that due to manual measurement and display differences, there may be slight differences between the individual products and the photos .