NYSE Composite Index - 1975

The following graph plots the year-to-date performance of the index for 1975 compared to the probability calculated by a random walk model.

Initial Value: 382.03 Hist. Volatility: 1.32% Annual Drift: 7% Final Value: 503.73 Percentile: 83%
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 1975 (what's this?).