A historical chart of an index price plots the value of an index over time and charts the related data, notes Bloomberg Business. Stock indexes that have available charts include the S&P 500, Dow Jones Industrial Average and the NYSE Composite Index.
A stock market index consists of a number of stocks that make up a given market or segment, notes the Houston Chronicle. When the prices of the stocks within the index change, the total index changes accordingly. A historical chart plots these price changes over time and graphs them. Generally, they divide stocks into small, mid, and large categories. Stock market indexes can also reflect performance in particular industries, including energy and health care. Plotting these indexes on a historical chart allows a user to compare financial performance across industries over a specific period. This historical chart contains a time frame, the current index value, the change in price over a particular period and other metrics that investors may find useful.