NYSE Composite Index - 1970

The following graph plots the year-to-date performance of the index for 1970 compared to the probability calculated by a random walk model.

Initial Value: 544.86 Hist. Volatility: 0.64% Annual Drift: 7% Final Value: 531.12 Percentile: 23%
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 1970 (what's this?).