Indicators
An indicator is a mathematical calculation that can be applied to a security’s price and/or volume fields. The result is a value that is used to anticipate future changes in prices.
A moving average fits this definition of an indicator: it is a calculation that can be performed on a security’s price to yield a value that can be used to anticipate future changes in prices. I’ll briefly review one simple indicator here, the Moving Average Convergence Divergence (MACD).
MACD
The MACD is calculated by subtracting a 26-day moving average of a security’s price from a 12-day moving average of its price. The result is an indicator that oscillates above and below zero.
When the MACD is above zero, it means the 12-day moving average is higher than the 26-day moving average. This is bullish as it shows that current expectations (i.e., the 12-day moving average) are more bullish than previous expectations (i.e., the 26-day average). This implies a bullish, or upward, shift in the supply/demand lines. When the MACD falls below zero, it means that the 12-day moving average is less than the 26-day moving average, implying a bearish shift in the supply/demand lines.
Figure 28 shows Autozone and its MACD. I labeled the chart as “Bullish” when the MACD was above zero and “Bearish” when it was below zero. I also displayed the 12- and 26-day moving averages on the price chart.

A 9-day moving average of the MACD (not of the security’s price) is usually plotted on top of the MACD indicator. This line is referred to as the “signal” line. The signal line anticipates the convergence of the two moving averages (i.e., the movement of the MACD toward the zero line).
The chart in Figure  shows the MACD (the solid line) and its signal line (the dotted line). “Buy” arrows were drawn when the MACD rose above its signal line; “sell” arrows were drawn when the MACD fell below its signal line.

Let’s consider the rational behind this technique. The MACD is the difference between two moving averages of price. When the shorter-term moving average rises above the longer-term moving average (i.e., the MACD rises above zero), it means that investor expectations are becoming more bullish (i.e., there has been an upward shift in the supply/demand lines). By plotting a 9-day moving average of the MACD, we can see the changing of expectations (i.e., the shifting of the supply/demand lines) as they occur.