The Collaborative International Dictionary
Extensometer
Extensometer \Ex`ten*som"e*ter\, n. [Extension + -meter.] An instrument for measuring the extension of a body, especially for measuring the elongation of bars of iron, steel, or other material, when subjected to a tensile force.
Wiktionary
extensometer
n. An electro-mechanical device for measuring changes in length of an object undergoing stress.
Wikipedia
Extensometer
An extensometer is a device that is used to measure changes in the length of an object. It is useful for stress- strain measurements and tensile tests. Its name comes from "extension-meter". It was invented by Charles Huston who described it in an article in the Journal of the Franklin Institute in 1879. Huston later gave the rights to Fairbanks & Ewing, a major manufacturer of testing machines and scales.