It involves comparing the boy’s and girl’s birth charts to check various levels of compatibility for marriage. A good astrologer will analyse several aspects such as harmony, physical compatibility, longevity, the strength of their bond, scope of prosperity, children, etc.
The planets; positions in the two horoscopes are studied to see if they are in harmony or conflict regarding the couple’s prospects of togetherness and the degree of compatibility.
A complex calculation and marriage compatibility is best done by a reputed astrologer who thoroughly studies various aspects before pronouncing the verdict. Online horoscope matching is only an approximate exercise and cannot be accurate like a personalised reading.