The Oliver No. 23-B reversible sulky plow is a horse-drawn riding plow that can be set to turn the soil to either side, thus allowing the use of highly-efficient plowing “patterns.” The machine was manufactured by the Oliver Chilled Plow Works of South Bend, Indiana, over the period from about 1917 through 1934. It has a very ingenious mechanism, the crafty geometry of which obscures its principles of operation. In this article I describe the Oliver 23-B and explain its mechanism and the way it supports the many special features of the machine. Some background is first given on the concepts of plowing.