MD is an index in BOLL, called standard deviation.

1) Calculate mA

Ma = sum of daily closing prices ÷N

2) calculate the standard deviation MD

MD= square root The sum of the two powers of (C-MA) of n days divided by n.

3) Calculate MB, UP and DN lines.

Mb = mobile authorization on the (n- 1) th day.

UP=MB+k×MD

DN=MB-k×MD

Middle rail (MB) Upper rail (UP) Lower rail (DN) Disk price (C) Days (N).