This calculates a one standard deviation price move based off of historic volatility and compares it to the historical price data to show how often an asset stays within its theoretical value of 68.2 percent.
Some things to be aware of are :
if you input the Implied volatility from option prices it uses that value over the whole historical data set, where as the hvol is re-calculated every day.
Also the whole model will overestimate short term price movement and underestimate the long term.