The setting method of bollinger bands is relatively simple. Generally, the middle track takes a mid-term moving average, and the default parameter is 2 days. The upper track takes the moving average plus 2 times standard deviation, and the lower track takes the moving average minus 2 times standard deviation. The standard deviation is a quantity to describe the risk in investment. The Bollinger Band with twice the standard deviation indicates that the probability of exchange rate fluctuation within the Bollinger Band is over 95.44%. The meaning and calculation formula of the standard deviation are discussed in the textbook "Love to Death" of all financial planners, which can be consulted by interested investors.