The movie demonstrates a solution of a typical construction problem: cut a segment into 2 equal segments. To solve the construction problem use a pen, pair of compasses and a ruler.
To cut a segment into 2 equal segments make 2 circumferences with equal radiuses and centers at the ends of the segment. Connect cross-section points of the circumferences by a line CD. The cross-point E of the line and the segment divides the segment into 2 equal segments.