Abstract: A system that has a graphical user interface (GUI) that allows a user to readily define and manipulate a transform function from one attribute, such as numerical value, to another attribute that is more understandable by by the user such as color, size or location. Special two thumb slider controls provide the transform functions. The two thumbs define break points for piecewise linear transform ranges. Further, the center transform range can be manipulated as a unit to show the user what happens if the range is maintained essentially constant but the break points are varied. The aid to visualizing characteristics otherwise hidden in large data sets, such as a monthly telephone bill of a large corporation, is very beneficial.