What tool is primarily used to measure angles?

A protractor is specifically designed for measuring angles, typically in degrees. It is a semi-circular or circular tool that has a graduated scale marked with the angle measurements. The functionality of a protractor allows users to align one side of the angle with the baseline of the protractor, making it easy to read the measurement directly where the other side intersects the scale. This precision and tailored design highlight why it stands out as the primary tool for angle measurement.

In contrast, a compass is used primarily for drawing arcs and circles and finding distances between points, while a ruler is utilized for measuring lengths or straight lines. A caliper, on the other hand, is best suited for measuring the depth and external or internal dimensions of an object, further distancing it from the task of angle measurement. These tools serve different purposes, making the protractor the appropriate choice for measuring angles.