One of the basic tenets put forth by Charles Dow in
the Dow Theory is that security prices do trend. Trends are often
measured and identified by "trendlines." A trendline is a sloping line
that is drawn between two or more prominent points on a chart. Rising
trends are defined by a trendline that is drawn between two or more
troughs (low points) to identify price support. Falling trend-s are
defined by trendlines that are drawn between two or more peaks (high
points) to identify price resistance.
Interpretation
A principle of technical analysis is that once a
trend has been formed (two or more peaks/troughs have touched the
trendline and reversed direction) it will remain intact until broken.
That sounds much more simplistic than it is! The
goal is to analyze the current trend using trendlines and then either
invest with the current trend until the trendline is broken, or wait for
the trendline to be broken and then invest with the new (opposite)
trend.
One benefit of trendlines is they help distinguish
emotional decisions ("I think it's time to sell...") from analytical
decisions ("I will hold until the current rising trendline is broken").
Another benefit of trendlines is that they almost always keep you on the
"right" side of the market. When using trendlines, it's difficult to
hold a security for very long when prices are falling just as it's hard
to be short when prices are rising--either way the trendline will be
broken.
Example
The following chart shows Goodyear along with
several trendlines.
Trendlines "A" and "C" are falling trendlines. Note
how they were drawn between successive peaks. Trendlines "B" and "D" are
rising trendlines. They were drawn between successive troughs in the
price.