In my experience of teaching Technical Drawing and Geometrical and Engineering Drawing over the past few years, I have noticed that when I arrive at the ‘Loci of Points in Mechanisms and Elementary Linkwork’ part of the syllabus, the pupils have difficulty in ‘seeing’ and understanding the various motions of the mechanisms and linkwork concerned. Of course, one can make a carefully drawn diagram for each example on the blackboard and let them learn it parrot fashion, but this is hardly what a good teacher aims at. It is much better for the pupil to comprehend fully what happens when each part of the mechanism or linkwork moves, and to see exactly where and how the locus is obtained.