Make Dependent Segments
Compare copying a segment length with copy-and-paste to copying the same segment using the compass tool. First, construct a segment like AB. Then select the segment and use the Edit menu to copy it and paste it to create a copy like A1B1. Next, use the compass tool, first define its radius (by clicking on points A and B) and then drag it to a new center for it, like C. Drag point A to change the length of segment AB. Does the copy A1B1 made with copy-and-paste change its length automatically? Does the radius CD change its length automatically when AB is changed? Why do you think this happens?