Bollinger bands – a popular technical indicator, which measures volatility and local price levels. It was made in 1980-s by a trader Jone Bollinger. The indicator consists of lines, which are build according to two standard deviations, according to simple sliding average. These lines constantly change and depend on the intensity of price cycling. More often, they are used as levels of supporting and resistance. But if the price is higher than the border of a band and then it falls inside, it is considered to be the end of positive tendency and it is a signal for exit.