Sometimes an article or an activity provides the stimulus for further investigations or explorations. Such was my reaction when I first read that a “collapsible compass” was used by Euclid instead of a “modern compass” to deduce his theorems in his book, Elements, which is considered one of the most influential works in the history of mathematics.

You may use this activity to challenge yourself to show the equivalence of the “collapsible compass” with the “modern compass,” or challenge your most capable students to do so. If not, you may separately view three separate proofs for establishing this equivalence while applying use of the collapsible compass for some basic geometric proofs.

This activity is perhaps best used near the end of a geometry course as a personal challenge or as an introduction to the history of mathematics.