Calibrating a Refractometer
— Always calibrate the refractometer in the lab, never in the field. —
- Open the daylight plate, and place a few drops of distilled water on the prism surface, holding the prism surface so that the water doesn’t run off.
- Gently close the daylight plate, checking that the water has formed a thin, even layer over the entire surface of the prism. If there are bubbles, or the plate is not entirely covered, re-open the daylight plate and add a few more drops of distilled water.
- Place the eyepiece to your eye and aim the refractometer towards daylight. Twist the eyepiece until the scale and numbers are in focus.
- Looking through the eyepiece, see if the blue/white dividing line crosses the scale at zero. If it does, than the calibration is complete. If the line is either above or below zero, the refractometer must be calibrated.
- Using the screwdriver found in the refractometer case, gently loosen the screw in the calibration ring.
- While looking through the eyepiece, slowly turn the calibration ring until the blue/white dividing line hits the zero on the scale. Once aligned, gently re-tighten the screw, taking care not to over-tighten.
- Open the daylight plate and carefully dry both the daylight plate and the prism surface taking care not to scratch either (dabbing with a paper towel works well).
- Return both the refractometer and screwdriver to the case, and the refractometer is ready to be used.