Secondary Progressions are based on the idea that the
movement of one day’s worth of movement defines one year’s
worth of developments. In short, the planets/points are advanced
one day’s worth of time for each year’s worth of time has passed
until the time-period being examined.
There is an important specification here. To get the angles and
cusps/powerpoints to advance at the right rate, the Solar Arc in right
ascension must be used.
Due to this being a slow, progressional system, the orbs for aspects
here have to be quite small. For sure, any aspects over 0° 15’ orb (for
events) don’t need to be considered.
This system works 100% as well in the converse as in direct motion.