Constructing Gann fan angles from swing extremes

Start from one swing pair

Gann angles are constructed by connecting a significant swing low to a significant swing high, or the reverse, then projecting a set of fixed geometric slopes from that origin. The chosen top or bottom is the swing extreme that anchors the whole construction.

A Gann fan is the family of geometric rays projected from that one significant high or low to map ranked trend lines through later price.

Fix the 1x1 line

The construction specifies nine named slopes and treats the 1x1 slope at 45 degrees as the primary trend line. The 1x1 line is that 45-degree Gann slope, used as the primary bull-versus-bear divider and as the intended support line in an advance.

Price above the 1x1 line is read as a bullish regime. Price below it is read as a bearish regime. In an advance, the 1x1 line is intended as primary support, and a break of that line is read as a major trend reversal.

Project the remaining slopes

An angle ratio is a Gann slope label that pairs units of price with units of time, such as 1x2 or 2x1. The nine construction slopes and their assigned degrees are 1x8 at 82.50, 1x4 at 75.00, 1x3 at 71.25, 1x2 at 63.75, 1x1 at 45.00, 2x1 at 26.25, 3x1 at 18.75, 4x1 at 15.00, and 8x1 at 7.50.

Most of those slopes are generated from the intersections of an 8x8 square and its outer box. The 3x1 and 1x3 slopes use a different derivation.

Applying the same measured slopes across a span of price produces the fan geometry used to identify broader-market bull and bear trends.