Nine types of kālamāna ( कालमान ) are used in traditional Hindu Calendar . Last (14th) chapter of Surya Siddhānta , the only extant ārsha text of Vedic Astronomy out of 18 original divya siddhāntas, is devoted entirely to this topic. Its first verse enumerates these nine types of mānas (measures) of kāla, hence that chapter is titled mānādhyāya.

Brāhma , Prājāpatya , Divya , Saura , Sāvana, Pitrya , Chāndra, Nākshatra and Gaurava or Bārhaspatya.
( ब्राह्म , प्राजापत्य , दिव्य , सौर , सावन , पित्र्य , चान्द्र , नाक्षत्र , गौरव या बार्हस्पत्य )

It is noteworthy that Sāyana or tropical system is never mentioned as any unit or system of measurement of time in any ancient Indian text. Tropical Year is a modern system starting in 1582 ADafter the Church accepted that the Julian Year should be changed to tropical. Many confused persons in India are trying to impose tropical Christian calendar on India using misinterpretation of Hindu scriptures. Therefore, elucidation of key terms in Hindu Calendar is presented below. First of all, the ancient calendar system is explained, starting from Surya Siddhānta, followed with current calendar systems prevalent in India.

साभार श्री विनय झा जी