The price graph of Abbott Labs illustrates these characteristics. During the MACD green uptrend that occurred between mid-January and early March, the 13-day exponential moving averages served as a formidable support line below which prices did not significantly penetrate.

Once the price bars pierced the 13-day exponential moving average in late March, it signaled the arrival of a relatively stiff retracement. During this retracement, which lasted throughout April, the 13-day exponential moving average served as a formidable resistance level, which prices did not penetrate at all.