Setup detail (connect two conducting sheets
to each power supply). The banana-to-pin adapter is inserted in the Comm terminal of the power supply; the ground wire from both multimeters is connected to this adapter. Make
sure all sheets are connected with the right screw head connected to the positive
terminal!
Make sure the nuts under the screw heads are finger tight, else voltages will fluctuate.
Use a sheet of the centimeter-rule paper for the potential map; it's easier to scale for the conducting surface used.