A line selected manually or by a rule in chart coordinates describes direction and possible reaction areas. It is not a path that the future price must follow.
StockCharts constructs an upward line through selected lows, with the second higher; a downward line runs through highs with the second lower. Point selection belongs to the method, not to the name Trendline itself. [1]
Two anchors at different times determine a straight line. StockCharts uses another touch as a confirmation convention. This convention is neither statistical evidence of reliability nor a guarantee that the next touch will hold. [1]
TradingView allows endpoint coordinates to be entered by price and bar number. To reproduce the line, retain both coordinates, the market and Timeframe; an image or label alone does not replace precise anchors. [2]
StockCharts distinguishes arithmetic and semi-logarithmic price axes. A straight line in linear prices represents equal price increments over equal time; on a logarithmic price axis it corresponds to equal multipliers. State the setting with the calculation. [1]
StockCharts notes that chart aspect ratio and displayed range alter the visible angle. A steeper picture therefore does not itself prove a stronger trend. Compare a defined price or percentage change over the same time unit. [1]
StockCharts explicitly distinguishes a line break from a trend change. Set a tolerance and decide whether the rule evaluates price during a candle or its Close. Extending a line is geometry, not new price information. [1]
TradingView offers alerts for crossing a line and settings for condition and frequency. A notification establishes that the configured condition was met; it is not itself an order, confirmation of reversal or guarantee of execution. [2]
TradingView warnings about lookahead bias and overfitting imply that an anchor must be known at the decision time in a test. If identifying a peak requires later candles, account for that delay and do not redraw the line retroactively to fit the outcome. [3]
Linear extension is not a forecast
Hypothetical anchors are at time t = 0 with price 100000 and at time t = 4 with price 104000 USD/BTC; t counts equal-length intervals. The slope is (104000 − 100000) / (4 − 0) = 1000 USD/BTC per interval. On a linear price axis, time t = 6 therefore gives 100000 + 6 × 1000 = 106000 USD/BTC. This is the extended line’s price, not a forecast of the actual price or an observed further touch.
For the clearest picture, read this entry together with Support and Resistance, Technical analysis, Timeframe, Price action, Breakout, Backtesting. The reverse links also lead from Price Channel, Market Structure Analysis, Head and Shoulders, Triangle Pattern.
01Does a third touch guarantee the trend’s validity?+
No. It is a convention for working with a line, not a verified probability of future developments. Anchor selection, touch tolerance and data availability at the time matter.
02Why does the same chart look steeper after resizing?+
The ratio of distances on the time and price axes changes, altering the on-screen angle. Resizing alone does not change the selected price and time coordinates; changing the price scale is a separate setting.