http://ipad41001.posterous.com/rectangular-coordinate-system-44737
Attempt to build something generic for a elementary school (K-12) topic.
Based on
http://en.wikibooks.org/wiki/Geometry_for_Elementary_School/Rectangular_coord…
Inspired by
http://twolivesleft.com/Codea/Talk/discussion/231/math-library#Item_1