Index value plot

http://www.cavemanforecaster.com/2009/04/case-shiller-housing-index-seasonal.html

This shows an index value plot for change in the Case-Schiller Index Value for home pricing over twelve months. Index value plots have a normal line, shown here by the 0.00% line, a standard line shown by the red dotted line, and an etching line which is shown here in blue. This type of graph is useful for showing how closely values lie to an agreed average or norm.