The commodity channel index (CCI) is an oscillator that indicates  when a currency is overbought with a figure higher than 100 or oversold with a figure less than -100. This indicator provides similar information to the Bollinger bands, it provides in numbers the relationship between the price, its moving average and deviations from that moving average:

Typical Price = (High + Low + Close) / 3
CCI = (Typical Price-Moving Average)/(0.015 x Deviation)

The constant 0.015 is present to bring the number to a figure which can be read easier.