For example: If you have Mars at 12 degrees Aries in your D1, the calculator knows that 12 degrees falls into the 2nd amsa (division) of Aries. It then moves Mars to the 2nd sign from Aries, which is Taurus, in your D9 chart.
In Vedic Astrology, the D1 chart is considered the body , but the D9 chart is considered the soul . Most professional astrologers refuse to make a prediction about marriage or life purpose without looking at the D9 first. d9 chart calculator