I am not a good blackboard artist, and my handwriting is abysmal. When writing words or equations on the board, I always used my father’s technique. First I said what I was going to write, and then I wrote it as best I could. Then I stepped back and translated my writing for the benefit of my students.
For many years, I taught a Natural Philosophy course for nonscience majors at Kenyon College, with a heavy concentration on optics and wave phenomena. Therefore, I often had to draw sine waves on the board. About 45 years ago, I made the sine wave template in Fig. 1.
It is 24 in. long and 12 in. high. I used 3/8-in.-thick plywood to strike a balance between its stiffness and weight as it was held by the handle against the board. In use, I first drew a straight line using the bottom...