Refractometer: Calibration

Calibrating a Refractometer
— Always calibrate the refractometer in the lab, never in the field. —

  1. 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.
  2. 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.
  3. Place the eyepiece to your eye and aim the refractometer towards daylight. Twist the eyepiece until the scale and numbers are in focus.
  4. 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.
  5. Using the screwdriver found in the refractometer case, gently loosen the screw in the calibration ring.
  6. 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.
  7. 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).
  8. Return both the refractometer and screwdriver to the case, and the refractometer is ready to be used.