Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s6.t2.4

v2.c12.s6.t2.4

Astronomical calculations require some moment of time to start with in order to predict future planetary positions. In accordance with this convention, the siddhānta works assume the commencing moment of Mahāyuga or that of some other Yuga and especially that of the Kaliyuga as the starting moment for calculation; and the Karaṇa works assume some particular year of the Śaka era as the commencing year. A Karaṇa works two however, can be found to have adopted Vikram Samvat along with the Śaka era. Thus the Karaṇa work Rāmavinod has adopted Akbar year along with the Śaka year, and the Phatteśāha Prakāśa has adopted the Phatteśāha year coupled with the Śaka year. The Vārṣiktantra (page 167), which is really a Karaṇa work has adopted the commencement of the Kaliyuga for the epoch for calculation, and the author has accordingly classed the work as ‘tantra’. Even than it has brought in some association with the Śaka era.