Step 1: Open the cover plate and place 2 or 3 drops of distilled water onto the prism

Step 2: Cover the plate and press lightly to ensure the water spreads evenly across the whole surface area

Step 3: Hold the refractometer towards a light source and look into the eyepiece

Step 4: If the boundary line between the upper blue field and the lower white field is not located on the 0 degree Celsius line, adjust the calibration screw until both lines meet

Step 5: Wipe the water from the prism and clean with a dry cloth