This ancient calendar is used today for setting religious dates in India and in other places where Hinduism is practised.
A day is measured from sunrise to sunrise. Days are grouped in units of ten. A year is divided into twelve lunar months of thirty lunar days each. A month is divided into two parts, the first governed by the full moon, and the second, by the new moon. Each day of a fifteen-day period is named by number. In southern India, as opposed to northern India, the new moon governs the first period, while the full moon governs the second.
The solar month did not have a fixed number of days, but was measured from the time the sun entered one zodiacal sign until it entered the next. The two systems were synchronized by adding a lunar month.