NYSE Composite Index - 1976

The following graph plots the year-to-date performance of the index for 1976 compared to the probability calculated by a random walk model.

Initial Value: 503.73 Hist. Volatility: 0.82% Annual Drift: 7% Final Value: 612.01 Percentile: 82%
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 1976 (what's this?).