Their primary use is to determine the direction of hte trend and to smooth out the noise. It is best to use 2 or 3, the number of periods is not that important (the difference between 20 or 30 days is minimal). Rule of thumb is that when the short is below the longer one, downtrend is strong. Some people use cross overs as buy or sell signals, for this you need to do your own research and conclusions. (Me, I don't use cross overs - they have too much whipsaw potential)
... View more