occur twice in a Cycle, or every 14 years. This happens when the Cycle crosses up from Low to High, and down from High to Low. The mid-point of the Cycle is the time of transition and chaos. This brings a shake up in Physically-based things as the Cycle changes. (Learn about Cycle Crossovers).
Figures #4-9a thru #4-9c on the next three pages show the 28-year Physical Cycle with Crossover years.