What the Useful Element Means in Qi Men: Settle It First, Then Read the Chart
In Da Liu Ren, which belongs to the same Three Styles, the first of the Three Transmissions is also called the active use, or the useful element, and in Qi Men the same step comes first. Choose the wrong useful element and every later layer fails to line up; the ways of choosing it differ between systems, so it is worth asking which set the other person is using.