First calipers date back to 6th century BCE, and they were utilized in ancient Greece as well as Roman empire. Calipers may vary in design and purpose. Some types look similar to drafting compass. Inside & outside calipers are suited for measuring gaps inside and distances outside of a given object respectively. After the readings are taken, the gap between the "legs" is measured by a ruler. Divider and oddleg calipers resemble a drafting compass even more - these tools are utilized for marking the material (most regularly metal). There is also a Vernier caliper, which resembles a ruler with jaws extending from it. Calipers often come with electronic gauges or indicators to make readings more detailed and understandable.