PURPORT

According to solar astronomical calculations, each year extends six days beyond the calendar year, and according to lunar calculations, each year is six days shorter. Therefore, because of the movements of the sun and moon, there is a difference of twelve days between the solar and lunar years. As the Samvatsara, Parivatsara, Idavatsara, Anuvatsara and Vatsara pass by, two extra months are added within each five years. This makes a sixth samvatsara, but because that samvatsara is extra, the solar system is calculated according to the above five names.