A strain gauge is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938.
The most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate.
As the object is deformed, the foil is deformed, causing its electrical resistance to change.
This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.