What is the COM jack labeled on a multimeter used for?

• A. Power input
• B. Return terminal for all measurements
• C. Display connector
• D. Signal ground

Answer: (B)

The COM jack is the common reference point and return path used by the meter for all measurements. The black probe typically plugs into COM and serves as the reference ground that completes the circuit for whatever you’re measuring. When you measure voltage, the meter reads the difference between the probe in the voltage/input jack and COM. For current, you connect the red lead to the appropriate current jack while COM still serves as the return path, completing the circuit. For resistance or continuity, the meter uses COM as the return point for the test current it applies.

So COM isn’t about power input or a display connector; it’s the fundamental return/reference leg that all measurements use to complete the circuit.