Laser extensometers are or mounted on a stand or built in the testing machine. In that last case a rail or an arm allows to put it away to a safe zone while not used. This extensometer works without any contact and then allows measuring the strain up to the breakage of the specimen.
2 reflectors set the base length at the starting of the test and the laser follows their moving up to the end of the test.
Laser extensometers are specially suited for long deformations.