The instrument used to make precise measurements of length is called a caliper. Calipers are versatile measuring tools that can gauge both internal and external dimensions as well as depths. They come in various forms, including digital and manual versions. A common type, the vernier caliper, features a sliding scale that allows users to achieve accurate measurements down to fractions of a millimeter or inch. Calipers are widely used in fields such as engineering, woodworking, and metalworking, making them an essential tool for professionals who require precise dimensional data in their work.