NYSE Composite Index - 1972

The following graph plots the year-to-date performance of the index for 1972 compared to the probability calculated by a random walk model.

Initial Value: 596.68 Hist. Volatility: 0.6% Annual Drift: 7% Final Value: 681.79 Percentile: 74%
Click on the image for the high resolution version.

The high to date and low to date prices of the stock plotted against a random walk model for 1972 (what's this?).