PRESIDIUM Gem Tester II Mode D'emploi page 121

Calibration procedure for Presidium Gem Tester II (PGT II)
1. Remove the Calibration Plug from the side of the housing to access to the calibration
potentiometers, C1 & C2 (Fig. 1.1 & 1.2)
Fig. 1.1 Fig 1.2
2. Adjust the indication needle so that it
moves to the center of the red "CAL" strip
by fully depressing the probe tip against
the "CAL" Disc while simultaneously
adjusting potentiometer C1 (Fig.2) with a
screw driver.
Fig. 2