The popularity of quote machines and fast trading requires a measurement of volume that can be used immediately to make decisions. Because total volume is not available on a timely basis to day traders, tick volume has become a substitute. Tick volume is the number of changes in price, regardless of volume, that occur during any time interval. Tick volume relates directly to actual volume because, as markets become more active. prices change back and forth more often. If only two trades occur in a 5-minute period, then the market is not liquid, regardless of the size of the orders that changed hands. From an analytic view, tick volume gives a reasonable approximation of true volume and can be used as a substitute. From a practical view, it is the only choice.