The Percentage Volume Oscillator (PVO) is a popular and free forex indicator for the MetaTrader 4 (MT4) trading platform. It is useful in measuring the strength of a trend by comparing the volume of a particular period to the volume of the previous period. It is calculated by subtracting the 26-period exponential moving average (EMA) of volume from the 12-period EMA of volume. The PVO can be used to identify potential reversal points in the market, as well as possible breakouts and trend continuation signals.