Drawing Ellipse on Chalkboard

Two spots are choosen to the the foci of an ellipse and then the ends of a large string are placed under both. Placing a piece of chalk on the inside of the loop the bottom and top of the elipse can be drawn by keeping the string taunt and moving along the edge. The top and the bottom should be done separately to avoid snapping the string on the magnets.
UCB Index: 
A+15+50
Demo Diagram: 

UCB Taxonomy:

Popularity: