Index of volatility or ratio of volatility

In connection with the variations of the prices in the share markets and in any market organized, the index of volatility is a measure of the change of the price relating to a certain lapse of time:

(Price superior - lower price) / Lower price

This variation coefficient or index be, naturally, negative if the prices have swooped, and positive if the prices have increased. For take the index in percentage is enough multiply the result bankrupted previous by 100.