Trend lines/support are some of the more simple yet effective inputs of any stock chart. These lines measure when a stock has moved out of the current trend or when the current slope of growth is no longer the same.
A couple days ago I posted a stock chart of Amazon. The chart did not show anything complex; however, the current trend upward was pretty evident. To keep the trade in play, the stock could not close below the current trend line (blue line).
The trend line held and the stock continued to move higher and the stock has moved from $211 to $231.
See more technical analysis skills and tools over at Chart School.