extensometer

noun

1. An electromechanical device for measuring changes in length of an object undergoing stress.

   “For the ground, that means using three primary types of equipment: ■ Extensometers to look for ground heave - the upwards movement of soil, which can occur at any stage. It is essentially the opposite of erosion and is often associated with clay-type soils which swell when wet. ■ Inclinometers, which measure slope movements. ■ Piezometers to measure water levels.”