<div class="htmlview paragraph">A brief resume of the history of power requirement studies of agricultural machinery at Ohio State University will, I hope, be of interest and helpful to establish a background for the work to be discussed later in this paper.</div> <div class="htmlview paragraph">The first portable belt dynamometer was built by the Department of Agricultural Engineering in 1922. It consisted of a four cylinder gasoline engine mounted in a balanced cradle. The torque reaction and speed was recorded on a gulley traction dynamometer recording device. A few over-all power requirement studies of a Rumely 22 x 36 thresher were made during the summer of 1923. A study of these first tests gave an impetus to the working out of a more comprehensive technique and program of testing of various types of belt driven agricultural machinery.</div>