Extensometer is a device that measures small changes in the length of an object. It is ideal fo stress-strain measurements. It increases the precision of the deformation measurements. The precision of measurements is increased on account of amplifying a small deformation by means of a system of levers. Ordinary scales are in fact a perfect extensometer. A small shift of about a few millimeters is transformed by a system of levers into a large swing of the scales pointer. The most perfect extensometers enable the measuring of the relative deformations of ~ 10-5 and amplify small signals by a factor of ~ (2/3) 103. Extensometer mainly falls into two categories such as contact and non-contact.