It is also called strain scale. It is used for measuring the strain of areas where it sticks. As it has wide variety of use, we will only talk about force and weighing. 

         Strain gages stuck on a load cell is shown in the picture below. As ?t ?s seen in the picture no. 1, strain gage changes when a force is applied to load cell. Its length varies as ?L, and its resistance as ?R.