Edith Clarke (February 10, 1883 - October 29, 1959) was an American electrical engineer. After college, Clarke taught mathematics and physics, briefly studied civil engineering at the University of Wisconsin-Madison, but left to become a human computer at AT&T. In 1921, she invented the Clarke calculator, a simple graphical device that solved equations involving electric current, voltage and impedance in power transmission lines. The device could solve line equations involving hyperbolic functions ten times faster than previous methods. No photographer credited, undated.