Secondary progression counts one day after birth as one year of life, which sends the Moon round the chart in about twenty-seven and a half years and back to where it started.

It is the most-used timing technique in modern Western astrology, largely because the Moon is the fastest thing in the chart and gives a reading that changes every two and a bit years. The cycle length is not arbitrary: it is the sidereal month, 27.32 days, read as 27.32 years.