Which instrument would you use to measure rotation speed of a shaft while it operates?

• A. NIBP
• B. Wire Stripper
• C. Needle Nose Pliers
• D. Tachometer

Answer: (D)

Measuring how fast a shaft is turning while it runs is done with a tachometer. A tachometer provides real-time RPM readings by sensing each rotation, either with a contact probe that touches the spinning part or a non-contact method like an optical/laser sensor that counts passes. This makes it ideal for verifying that speed stays within the design spec and for spotting issues such as slipping belts, bearing problems, or governor faults.

The other tools shown aren’t meant for measuring rotation. A blood pressure device measures arterial pressure, while wire strippers and needle-nose pliers are hand tools for wiring and manipulation, not speed measurement.