The Momentum Indicator

Momentum measures the amount that a price has changed over a given time span. The ratio is calculated by the following formula:
Momentum = (C/Cn)*100

where C is the most recent closing price, and Cn is the closing price n periods ago.

Trend followers buy when the momentum indicator bottoms and turns up, crosses above some absolute threshold, crosses above some moving average of itself, or shows some positive divergence relative to price. Trend followers would sell when the opposite conditions apply.