NYSE Composite Index - 1979

The following graph plots the year-to-date performance of the index for 1979 compared to the probability calculated by a random walk model.

Initial Value: 566.96 Hist. Volatility: 0.74% Annual Drift: 7% Final Value: 655.04 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 1979 (what's this?).