Robinair 75240 Coolant and Battery Refractometer Robinair's Coolant and Battery Refractometer is designed for use in measuring the freeze point of propylene or ethylene glycol based cooling systems and for checking the strength of electrolyte solution batteries Precision instrument features high-quality optics with ultra smooth focusing to ensure reliable, accurate test results When a liquid (such as coolant or charging liquid) is placed on the tools prism, the light passing through it is bent - the more concentrated the liquid, the more the light will bend Scale range: -60 degrees Fahrenheit to +32 Fahrenheit Complete kit includes refractometer with rugged aluminum housing, eyedropper, screwdriver, vial of distilled water, cleaning cloth, foam lined rigid plastic case, and more