Map buffers
Define the numeric values that will be given to the different buffers. This is call “Mapping buffers”, basically once all is done, MQL5 will return the values of the buffers in the order mentioned here. In the case of BB, the upper buffer will be given 0 and the lower buffer 1. If at any later case you need to use the values of the upper band, you need to call the indicator and its buffer 0, if you want the values of the lower band, you will call the indicator and its buffer 1.