Convergence/Divergence (MACD)
Developed by Gerald Appel, Moving Average Convergence/Divergence (MACD) is one of the simplest and most reliable indicators available. MACD uses moving averages, which are lagging indicators, to include some trend-following characteristics. These lagging indicators are turned into a momentum oscillator by subtracting the longer moving average from the shorter moving average. The resulting plot forms a line that oscillates above and below zero, without any upper or lower limits. MACD is a centered oscillator and the guidelines for using centered oscillators apply.
More: http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:moving_average_conve
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.