Which tool can be used to measure the area of a P-V diagram?

The planimeter is specifically designed for measuring the area of two-dimensional shapes, such as the area under the curve in a pressure-volume (P-V) diagram. When analyzing P-V diagrams, the area enclosed by the curve represents work done in thermodynamic processes. The planimeter functions by tracing the perimeter of the area in question, allowing it to calculate the enclosed area accurately.

In contrast, the other listed tools serve different purposes. A caliper is primarily used for measuring the distance between two opposite sides of an object, making it unsuitable for area measurement. A micrometer provides high-precision measurements of small objects, typically in terms of thickness or depth rather than area. A pressure gauge measures the pressure of gases or liquids, but it cannot provide any information about area measurement on a P-V diagram. Therefore, the planimeter is the correct choice for measuring the area represented in such diagrams.