The Rank Correlation Index (RCI) is based on an analysis algorithm by Spearman. It uses a combination of price change data and time change data to identify potential changes in market sentiment, thereby exposing turning points.
Zero crossings are seen as buy and sell signals, with tops and bottoms yielding overbought and oversold information.
I have coded a version for Forex Tester and also one for MetaTrader 4. Both are available for $14.97 each! Check 'em out~