extensometer

/ˌɛkstɛnˈsɑmɪtər/
noun
  1. A device used to measure small changes in the length of an object, especially to test how materials stretch under stress.
    • The bridge's safety was monitored with extensometers that detected any tiny deformations in the metal supports.
    • In the lab, we used an extensometer to check the elasticity of the rubber sample.
    • The engineer attached an extensometer to the steel beam to measure how much it stretched under the heavy load.