Which instrument tests micrometer calibration?

• A. Gauge blocks
• B. Calipers
• C. Dial indicators
• D. Rulers

Answer: (A)

Gauge blocks provide the known reference lengths used to check and calibrate a micrometer. They are manufactured to extremely tight tolerances and are traceable to national standards, with lengths certified at a controlled temperature (usually 20°C). This makes them a reliable, repeatable standard for verifying the micrometer’s readings.

To test the micrometer, choose a gauge block with a length within the micrometer’s measuring range, clean it, and place it between the micrometer’s anvils. Close the spindle gently, take a reading, and compare it to the block’s nominal length. If the reading matches within the micrometer’s tolerance, the instrument is calibrated; if not, it needs adjustment or servicing. Using several block lengths across the range also helps verify the micrometer’s linearity.

Other tools like calipers or rulers don’t provide the same precise, certified reference, and dial indicators measure displacement rather than a fixed length, so they aren’t used as the primary standard for calibrating a micrometer.