A technical momentum indicator that is used to illustrate the relationship between the rate of an asset's price change and its volume. This indicator attempts to identify the amount of volume required to move prices. Generally a value greater than zero is an indication that the stock is being accumulated (bought) and negative values are used to signal increased selling pressure.
A high positive value appears when prices move upward on low volume. Strong negative numbers indicate that price is moving downward on low volume.

A moving average of the indicator can be added to act as a trigger line, which is similar to other indicators like the MACD. Transaction signals can be generated when the indicator crosses over a 9-day moving average, but are generally made when the indicator crosses over the zero line. Traders use the smoothed version of this indicator in an attempt to eliminate false signals.