Hey-Hey!!!
For this you ignore the mu output. Put the ammeter or sensing resistor in series with a 9V battery. + to the upper drain and - to the plate end of R-3. Watch the meter and adjust until the CCS is passing the 15 mA of current. If you use a sense resistor, use Ohm's Law to determine curent. If you use the mA function then you'l get the reading directly. It will probably come in when R-3 is ~150R or so.
Call if you wish, I will talk you through it.
regards,
Douglas