The Tetrad tool is made up of four points. As it relates to trading, two points of the Tetrad are used to identify the two extreme points of a range in price and time. The two points of the range are then used to plot one side of a square with angles of 90 degrees each. Reversals often take place when the market reaches the extreme right tip of the square.
This is a companion discussion topic for the original entry at https://www.optuma.com/kb/optuma/tools/geometric/tetrad