Hand held Refractometer - instructions for use
Lift the plastic cover plate, squeeze the juice from a single grape on to the prism surface, lower the plastic cover so that a thin film is formed on the prism. Point the refractometer towards strong light. Twist the eyepiece until the scales are in focus. Read off the scale at the white/blue transition.
A drop of the stirred juice, after pressing, can be used to measure the natural alcohol %.
Use a table to convert °Oeschle (or Brix = % mas Sacch) to % alcohol.
Use a paper tissue to wipe the refractometer dry, do not wash with water.
Initially the refractometer will be calibrated correctly. You should never need to alter it, unless maybe you drop it. Then ask your WSB officer to check against his model using the same juice, and adjust the recalibration/correcting screw using the tiny screwdriver supplied.