Invented by Edward Simmons and Arthur C. Ruge in 1938, the strain gage utilizes the principles of electrical conductance to measure a physical force. The ability of a metal to stretch or compress is the characteristic that allows a strain gage to operate. Today, strain gages are commonly used in experimental fields for stress analysis. For example, their ability to measure fatigues in metal is important in the aerospace and automotive industries for ensuring safe and efficient machinery. By testing the amount of strain a material can take, engineers can determine the strongest and best materials for machines like automobiles and airplanes.