Theodolite

A theodolite is a tool for measuring angles between two places (or points) from one place. They are usually associated with surveying. They are often mounted on a special kind of tripod.Daumas, Maurice 1989. Scientific instruments of the seventeenth and eighteenth centuries and their makers. 1989. Portman Books, London. ISBN 978-0-7134-0727-3Anita McConnell 1992. Instrument makers to the world. ISBN 978-1850720966

They are usually a telescope on a mount that can move horizontally (left and right) and vertically (up and down). The mount has a scale where the readings are taken, usually in degrees for older models and arc minutes or arc seconds for newer models. The telescope normally has a crosshair to make it easy to align it to the points to be surveyed. The theodolite was the first tool that could do vertical and horizontal measurements in the same device.

Most modern theodolites are electronic and the readings are read from a digital display.

A transit is a kind of theodolite that can do a whole circle vertically and horizontally.

 References 

Category:Measuring tools