The core of this predictive technique is the Sun: its individualized progressed motion approximating a day-for-a year captures one's progress throughout life time.
To calculate the Solar Arcs, we use the position of the Secondary Progressed Sun. The Secondary Progressed Sun's position is the Sun's position a specific number of days after birth, to correspond to the same number of years in life. As the Sun's average daily motion is of one degree, during each year of live the Secondary Progressd Sun will move one degree. This way, we can easily calculate Secondary Progressed Sun's position by adding the person's age to the natal Sun's position.
The technique of the Solar Arcs: we calculate the Secondary Progressed Sun' position. Then we substract the natal Sun' position and we get the Solar Arc increment for that time of the native's life. And then we advance every planet, the nodal axis, the Ascendant and the Midheaven with this increment, by addingthe Solar Arc to the natal planet's position.
The inner logic of this technique: the primal symbol of life development, the Sun, is being shared with every symbol in the horoscope.
The Solar Arcs may be used forward and backward in time.
Since the Solar Arcs use a generalization of one degree=one year, the orb for the Solar Arcs is one degree or one year.
Many times, the Secondary Progressed Moon can refine the specific time of arc completion and there will almost invariably be a major transit to trigger the Solar Arc.
In the Solar Arcs theory only the so-called "hard aspects" are used: conjunction, square, opposition, semisquare, sesquiquadrate.
This article presented information on the Solar Arcs as teached by Noel Tyl in his great book (a must read for any astrologer) "Solar Arcs: Astrology's most successful predictive system".