Trendlines are easily recognizable lines that traders draw on charts to connect a series of prices together or show some data's best fit. The resulting line is then used to give the trader a good idea of the direction in which an investment's value might move. Trendlines indicate the best fit of some data using a single line or curve.
A single trendline can be applied to a chart to give a clearer picture of the trend. Trendlines can be applied to the highs and the lows to create a channel. The time period being analyzed and the exact points used to create a trendline vary from trader to trader
Limitations of a Trendline Trendlines have limitations shared by all charting tools in that they have to be readjusted as more price data comes in. A trendline will sometimes last for a long time, but eventually the price action will deviate enough that it needs to be updated. Moreover, traders often choose different data points to connect. For example, some traders will use the lowest lows, while others may only use the lowest closing prices for a period. Last, trendlines applied on smaller timeframes can be volume sensitive. A trendline formed on low volume may easily be broken as volume picks up throughout a session.