This indicator is a ported MQL5 indicator from http://www.mql5.com/en/code/2134.
Formulas:
AO_Fast = MVA(100*(Short_EMA/Medium_EMA-1), AO_Fast_Period),
AO_Slow = MVA(100*(Medium_EMA/Long_EMA-1), AO_Slow_Period).
Download:
If both Fast and Slow values are greater than Zero Line, Green Arrow up
If both Fast and Slow values are less than Zero Line, Red Arrow down