Milwaukee Salinity Refractometer with ATC by Milwaukee Instruments MR100ATC. **** PRODUCT MANUAL **** The MR series refractometers are precision optical instruments used for measuring aquarium water salinity. They work using principle of light refraction through liquid. When passing light through a liquid the refracted angle will be shown on the scale determining the amount of salt in the water. Very easy to use; simply place one drop of water on the prism and read the results on the scales immediately. They have adjustable focus, easy to read numbers for good resolution, and zero adjustment screw for calibration. These refractometers have Automatic Temperature Compensation feature and are suitable for application where the temperature of the samples vary. Each refractometer comes in a hard protective carrying case and includes calibration screwdriver, pipette, and instructions.