These techniques are more appropriate for larger trends and pinpointing eventful years. Although tertiary and minor progressions are based on a similar principle, they should not be confused with one another. Unlike secondary progressions which move one day in the ephemeris for a year of like, tertiaries are calculated so that each day after birth is equivalent to a month of one's life. 12 days equals one full year. Following the day of birth, each return of the Moon to its zodiacal position is equal to a year of life.
Minor progressions move along at a faster rate than tertiary progressions.
I find them to be particularly useful indicators of prominent issues in a person's life when used in connection with transits. The Moon's movement through the houses is approximately one house or sign per month. This motion shows additional monthly themes along side of the Sun's monthly transits through the houses. Instead of using the longitudinal degrees, the rate of directions are from the ascensional times, or the rate at which a sign at a particular geographical latitude rises in the East. The Ascendant is typically the starting point for primary directions, but other planets can be used as well.