Wolfram Demonstrations Projecthttp://demonstrations.wolfram.com/An Open Resource of Interactive Mathematica VisualizationsCopyright 2009 Wolfram Demonstrations Project & ContributorsProportional Quantitieshttp://demonstrations.wolfram.com/ProportionalQuantities/]]>http://demonstrations.wolfram.com/ProportionalQuantities/Ratio Notationhttp://demonstrations.wolfram.com/RatioNotation/]]>http://demonstrations.wolfram.com/RatioNotation/