AMMA's formula is:
AMMA[i] = ((AMMA.Period-1)*AMMA[i+1] + Close[i])/AMMA.Period;
A 25-day Average Modified Moving Average is employed as a filter. This was defined by Maxwell in "Commodity Futures Trading with Moving Averages."
AMMA is multiplied by 24, then today's close is added and the sum divided by 25.