Hold the instrument up to the light and look through the eyepiece. Rotate the eyepiece to focus the scale. Thoroughly clean the prism and flap immediately after use with water or other suitable solvent and dry with clean tissue.The prism surface could be damaged by strong alkalis or acids if left in contact for long periods of time. Clean samples from the prism as soon as practicable.Wiping the prism surface occasionally with alcohol will remove any build-up of oils left from the samples. Lift the flap, drip sample onto the prism then close the flaporuse the dribble feature; drip sample into...

The Horizon Line The horizon line is the line which is created between the light and the dark areas in the viewpiece of the refractometer. If you have new clean coolant mix, then the line should be fairly sharp. As the coolant ages and as more tramp oil is beaten into it, then the line becomes less distinct. If you let your coolant go long enough, you will not be able to see any line at all, as there will be only one big blurred area in the field of view. Once it is hard to distinguish the horizon line, it may be time to think about changing the coolant. Using water only (distilled whenever available),...