If the needle of an analog voltmeter moves below zero, what should you do?

• A. Swap the voltmeter leads
• B. Increase the range
• C. Replace the battery
• D. Short the circuit

Answer: (A)

When an analog DC voltmeter shows a reading that goes below zero, it’s usually a matter of polarity. The moving-coil mechanism inside the meter responds to current direction, so if the leads are connected the wrong way around, the needle will deflect to the negative side even though the voltage is positive.

To fix this, switch the test leads: connect the meter’s positive lead to the circuit’s positive point and the meter’s negative lead to the circuit’s negative point. The same voltage magnitude will then appear on the positive side of the meter’s scale, provided the range is appropriate and you’re measuring DC.

Increasing the range won’t correct a polarity sign, and replacing the battery isn’t a solution for a polarity issue. Shorting the circuit is dangerous and unnecessary.