"A day for a year" - see how your chart has moved over time. The progressed Moon shows emotional cycles, progressed Sun - life stages. Each sign change is the start of a new era.
The secondary progression formula is "a day for a year" - your progressed chart at age 30 is your natal chart calculated 30 days after birth. It shows inner psychological development, not outer events. Primary use: watch when progressed Moon changes sign (every 2.5 years - a new emotional theme) or Sun (every ~30 years - a new life cycle).
