class_docstr: MeanDeviation (alias MeanDev)
  
  Calculates the Mean Deviation of the passed data for a given period
  
  Note:
    - If 2 datas are provided as parameters, the 2nd is considered to be the
      mean of the first
  
  Formula:
    - mean = MovingAverage(data, period) (or provided mean)
    - absdeviation = abs(data - mean)
    - meandev = MovingAverage(absdeviation, period)
  
  See:
    - https://en.wikipedia.org/wiki/Average_absolute_deviation
code: def _plotlabel(self):
      plabels = [self.p.period]
      plabels += [self.p.movav] * self.p.notdefault("movav")
      return plabels
  
file_path: backtrader/backtrader/indicators/deviation.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from .None import Indicator, MovAv
label_desc: Use image node_id 1 for calling the MeanDeviation obj's underlying member method code with example usage: obj._plotlabel() and returns: plabels