Drawing trendlines is an art, not a science. Rarely will 2 people draw them the exact same way. With that in mind, the essence is to draw one that gives you an accurate feel for that stock (i.e., market direction, support, resistance, etc). Some people use the extremes (highs and lows of the day), some people use the main candle body (open and close), some people mix them up according to their experience. Author Tom DeMark tried to offer a "scientific" approach so that 2 people would always draw the same trendline, but his methodology is not generally accepted, so it remains an art.