Technicians use trendlines to identify trends and determine when they end or reverse. The only problem with traditional trendlines is they are subjective — 10 traders could look at a chart and draw 10 different trendlines. Proper trendline application and analysis require consistent, objective rules.

The TD–Line technique was developed by Tom DeMark and is detailed in his books The New Science of Technical Analysis (John Wiley & Sons, 1994) and DeMark on Day Trading Options (McGraw–Hill, 1999). The complete methodology includes objective rules for plotting these trendlines, rules for validating them, and rules to determine whether to trade or fade a trendline break.