This chart shows Volatility for Darden Restaurants, defined to be the price range as a portion of the average price:
So, to derive the Daily Volatility on 6/26/2009 of 2.5%, the price range for the day (0.83) was divided by the average price (32.47). The Daily Volatility is obtained by dividing the daily range by the daily average. A longer Volatility period such as Weekly Volatility is obtained by dividing the weekly price range by the weekly mean price. It is important to avoid confusing this with the weekly average of the daily volatility, which is a completely different concept.
For reference, the price is plotted in red. Volatility, as measured through various intervals, ( Daily, Weekly, Monthly and Quarterly) is plotted according to color.
Investors often make a distinction between the concept of Volatility, and the concept of Risk. Academics define them to be exactly equivalent, but as can be seen here, there is good reason to distinguish between the levels of volatility or risk experienced across different time frames. Average Daily Volatility over the history of DRI has been 3% in contrast to the Average Quarterly Volatility of 27%.
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