Three sheets. All work with a mouse or a trackpad; none has been tested on a touchscreen.
The angle at the centreEuclid III.20, built by hand and then tested. You draw the figure with the instruments, follow the proof a line at a time, and then find the two cases Euclid does not write. The exterior angleEuclid I.32, the one theorem III.20 cites. Draw a triangle, carry a side on, draw the parallel, and watch the two far corners fill the angle outside. A blank sheetThe instruments on their own, with nothing to follow. Four of Euclid's constructions are offered if you want something to aim at — I.1, I.9, I.10 and III.1.