Which instrument provides measurements on a moving scale with a small slider and is commonly used to measure thickness and diameter?

• A. Vernier caliper
• B. Dial caliper
• C. Micrometer
• D. Magnetic base

Answer: (A)

The instrument that uses a fixed main scale with a sliding, smaller scale to give precise readings is the Vernier caliper. Its design includes a main scale on the beam and a sliding Vernier scale on a small slider. As you tighten the jaws around an object, you read the measurement by aligning marks on the Vernier scale with those on the main scale, which lets you determine thickness or diameter with fine precision beyond what the main scale alone could show. This combination of a moving scale and a small slider is what makes the Vernier caliper ideal for measuring thicknesses and diameters.

A dial caliper, while also a sliding caliper, uses a dial readout rather than the Vernier scale, so it isn’t described by a “small slider” with Vernier markings. A micrometer relies on a screw and thimble mechanism with a fixed sleeve scale rather than a movable Vernier slider across a main scale. A magnetic base is just a stand or attachment, not a measurement instrument.