A form of technical analysis based on the ideas that the market is geometric and cyclical in nature. A Gann fan consists of a series of diagonal lines called Gann angles, of which there are nine. These angles are superimposed over a price chart to show a security's support and resistance levels. The resulting image is supposed to help technical analysts predict price changes. Although once drawn by hand, today Gann fans can be drawn with software programs.
Gann Fans were developed by W. D. Gann, who was also known for his accurate financial predictions, called the Gann studies, in the early 1900s. Gann's ideal angle was a 45 degree angle based on his ideal balance of time and price. However, because the construction of a Gann fan relies heavily on subjective choices made by individual traders, the chart may be limited in its usefulness and accuracy. The three premises Gann based his theory on were: i) price, time and range are the only factors, ii) cyclical markets, and iii) geometric market design.