Instruments:

Several methods used for linear measurements of distances between two points on the earth's surface can be broadly classified (based on instruments used) as:

(a) Direct measurements through chain or tape,

(b) Measurements by optical instruments and/or with calculation, e.g. tachometry or triangulation, substance bar, telemeter etc. and

(c) Electronic devices, e.g. Geodimeter, Distomat, EDM etc. based on propogation, reflection and reception of radio/light waves.

The most generally used technique of measuring linear distances particularly within field and engineering surveys is through chain or tape. This process of measuring distances through chain is termed chain surveying.