The Relative Volatility Index was developed by Donald Dorsey. It measures the direction of volatility on a scale from 0 to 100%. It is similar to the Relative Strength Index except that RVI is based on the standard deviation of high and low as opposed to the RSI which is based on the change in close.
Because it measures a different set of market dynamics, it is usually used to confirm signals generated by momentum and trend-following indicators. A buy signal in one of these indictors is confirmed when RVI is greater than 50%. A sell signal is confirmed when RVI is less than 50%.