A basic principle of technical analysis is that security prices move in trends. We also know that trends do not last forever. They eventually change direction and when they do, they rarely do so on a dime. Instead, prices typically decelerate, pause, and then reverse. These phases occur as investors form new expectations and by doing so, shift the security’s supply/demand lines.
The changing of expectations often causes price patterns to emerge. Although no two markets are identical, their price patterns are often very similar. Predictable price behavior often follows these price patterns.
Chart patterns can last from a few days to many months or even years. Generally speaking, the longer a pattern takes to form, the more dramatic the ensuing price move.
Double Top and Bottom Pattern
A double top occurs when prices rise to a resistance level on significant volume, retreat, and subsequently return to the resistance level on decreased volume. Prices then decline marking the beginning of a new down-trend.
A double bottom has the same characteristics as a double top except it is upside-down.
The following chart shows Caterpillar and a double bottom pattern.