A trendline is one of the most basic but established utility in charting. A break in trend caused by the penetration of the trendline results in either an actual trend reversal or a slowing in the pace of the trend. Although it is hard to know which alternatives will develop, there are three guidelines that can assist us in our evaluation.
The trend length is a crucial factor to take into consideration. A short length trendline occurring over 1-3 weeks are only of minor importance. If the trend extends over a longer period of 1 month to 36 months, its trend violation will signify a crucial juncture point. So by analogy, long trends equals big signal, short trend equal small signal.
-The number of times the trendline has been tested
A trendline is formed by a dynamic area of support and resistance. The more times the trend is tested, the more authority it has. Also note that a close encounter approach to the trend is almost as important as an actual test. If a line gains significance from the fact that it has been tested, the extended line will become equally as important.
-The angle of ascent or descent
All trends will eventually be violated. A steep trend is of lesser significances because they are likely to be ruptured more quickly. Steep trend violation is usually assumed to be a short corrective movement and is usually represented to be a continuation rather than a reversal break. A gradual trend violation holds more authority and is a more plausible candidate for a trend reversal.
Hope that these few pointers can make your trendlines evaluation more useful and efficient.