Learn basic technical indicator Bollinger Bands.
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Bollinger Bands

  Bollinger Bands is the range where the underlying asset remains at specific probability. Bollinger Bands is defined by moving average (SMA or EMA) in a specific period[X] and standard deviation in the same period[X]. In case of the range "(Moving Average) +/- 2 x (St.Dev)", probability of the price in the range is 95.45%. (With some theoretical preconditions)

  Bollinger Bands is represented as Bollinger Bands[X, Y] with the parameters X (calculation period) and Y (multiple number to St.Dev). For example, in 1 min scale, calculation period last 240 mins and the multiple number 3, it will be represented as Bollinger Bands[240, 3].

Bollinger Bands[X, Y] calculation formula

  In order to obtain Bollinger Bands, define

   1) Time scale for the historical data
   2) Calculation period[X] for moving average and standard deviation.
   3) Multiple number[Y] to the standard deviation.

  [Calculation sample]
   1) 1 min scale
   2) Last 240 data points (Last 240 mins)
   3) The multiple number is 3

  Bollinger Bands calculation sample on spread sheet.