I'll save Robb the effort because I once asked him the same question. His ranges are based on the 20 day average of each individual range (high - low).
Excel has an averaging formula ie: "=AVERAGE( : )" where you put the cell address of the first and last lines of data in the blanks so if you can import the daily ranges into excell its very easy to calculate the average. We use e-trade pro and copy the tabular history of whatever stock we are looking at straight into excell.
