Extensometers An extensometer is a device that is used to measure small/big changes in the length of an object. It is useful for stress/strain measurements and tensile tests Hylec Controls can supply the Video and Laser Speckle Extensometers from Messphysik used for measuring the tensile extension of metals and other materials remotely. Clamp-on extensometer devices can also be supplied that physically attach to the materials under test.