Something else you might want to know.....

Volume is a measure of trading activity. On stock exchanges, volume is the number of shares trading hands over a given period of time. Not all exchanges count volume in the same manner; on the NYSE, a transaction of 100 shares adds 100 to the volume tally, but on the Nasdaq , the same transaction increases the volume by 200. The Nasdaq method is referred to as double-counting because the buy and sell are viewed as distinct transactions. As a general rule, markets that are completely electronic double-count, whereas physical markets do not.