Error in "THC Troubleshooting flow chart"?

from flow chart : “Make sure to plug back in your USB cable to
the electronics box and remove your plasma cuter Work Clamp from the
machine frame. Using a Digital Multmeter set to DC Voltage, touch the
black probe to the GND pin and the red to the A1 pin on the top pins of
the THC unit as shown in the picture below and perform a straight cut
while measuring this voltage.”
QUESTION: How do I cut without ground (no work clamp from machine) ?