Which tool is commonly used for taking precise measurements in assembly projects?

The caliper is widely recognized as a critical tool for taking precise measurements in assembly projects due to its ability to measure both internal and external dimensions as well as depths accurately. It features a sliding scale, which allows users to take measurements down to very fine increments, typically in both metric and imperial units. This high level of precision is essential in aerospace assembly, where even small measurement errors can lead to significant issues, affecting safety and performance.

In contrast, while protractors can measure angles, they don't provide the precision needed for linear measurements in assembly. Compasses are primarily used for drawing circles or arcs and do not serve the purpose of measuring dimensions accurately. A square is used to check the squareness of components and set angles, but it is not specifically designed for precise linear measurements, making the caliper the superior choice for this application.