What is the purpose of using a caliper?

Using a caliper is primarily for measuring the distance between two opposite sides of an object, which is essential for achieving precise dimensions in machining and engineering tasks. This type of measurement is crucial for ensuring that individual parts fit together correctly and meet the specified tolerances.

Calipers can measure outside dimensions (external jaws), inside dimensions (internal jaws), and even depths (depth probe), providing versatile applications in various machining scenarios. Accurate measurement is fundamental in the machining process, where slight deviations can lead to flaws in assembly or functionality of the final product.

The other options, while they relate to machining in varying contexts, do not define the primary purpose of a caliper. For instance, measuring temperature is not a function of calipers, nor does it play a role in calibrating machine tools or holding workpieces, which are tasks suited for other tools and instruments. Therefore, the clarity and focus of a caliper's role in measurement establish it as the correct answer.