A method of deducing solar wind speed from magnetic observations of the Sun was verified in 1989 using 22 years of observations. This paper traces the evolution of this method from its birth in 1974 to its current use as a space weather forecasting technique. This paper is taken from an invited talk at the joint session of the Historical Astronomy Division and the Solar Physics Division of the American Astronomical Society during its 224th meeting in Boston, MA, on 3 June 2014.