Our methodology for historical volatility calculation is the annualized standard deviation of the first difference in the logarithmic values of nearby futures settlement prices. Mathematically,

The following example illustrates how we arrive to the volatility data for Rough Rice Futures contract. During March 2008, the realized (historical) volatility for Rough Rice is 2.2% on a daily basis. As volatility is usually described in annualized terms, we use a factor of square root of 252 (estimated number of trade days in a year) to annualize the historical volatility to 35.4%.