Hand Held Refractometers are used to determine concentration level of semi solid and fluid based substances by passing natural light through the tested samples. As per the operating principle of these instruments, the speed of any passing light (when it goes through sample) tends to change as per the thickness of tested sample. The ray of passing light alters its direction with the change in its speed. These Hand Held Refractometers are also used to determine ration of heat exchanging fluids and anti freezing agents used in automotive arena.