Which instrument has a shaded dial that, when used with a mirror, allows the operator to read the last digit correctly?

• A. Last word indicator
• B. Dial caliper
• C. Vernier caliper
• D. Magnetic base

Answer: (A)

Reading the smallest increment accurately often uses a feature that makes the final digit unambiguous, reducing parallax errors. The instrument with a shaded dial designed to be read through a mirror fits this purpose perfectly: the shading highlights the last digit, and the mirror lets you view the reading without the distortion that comes from looking at the dial head-on. This setup directly supports obtaining the correct last digit.

Dial calipers and Vernier calipers rely on direct line-of-sight readings of scales, with the Vernier requiring alignment between scales to interpolate the value. They don’t employ a shaded dial or mirror-reading technique for the last digit. A magnetic base is simply a mounting accessory, not a reading instrument.