The calibration process determines the minimum frequency at which the ED722 will operate.

1. Set the [RATE] control to minimum
2. Fit jumper JP1 in to the 'CAL' position
3. Monitor the output of U2 at test point TP1 using a multimeter set to the 1V DC range
4. It will probably exhibit a tendency to drift positive or negative and the voltage will eventually settle at +12V or -12V
5. Reset the output voltage by momentarily shorting JP2
6. Adjust P4 until the voltage remains stable with minimal drift for a period of several seconds
7. Repeat steps (5) and (6), progressively switching the multimeter to more sensitive ranges, until the drift is only a few millivolts over several seconds
8. Fit JP1 in to the 'RUN' position and ensure JP2 is open