Construction Using Isometric Perspective
An illustration showing how to use isometric perspective. "This kind of perspective admits of scale measurements the same as any ordinary drawing, and gives a clear representation of the object. It is easily learned. All horizontal rectangular lines are drawn at an angle of 30°. All circles are ellipses of proportion, as shown."
Albert A. Hopkins Scientific America: Handy Book Of Facts And Formulas (New York: Munn & Co., Inc., 1918) 37
Courtesy the private collection of Roy Winkelman