Rashtriya Panchang
The very fact that the calculations of the almanac are fully done with the help of computers show the accuracy of the renderings and therefore the timing of the puja and parvan for different occasions also are free from any mistake. Hence the Indian national calendar (Rashtriya Panchang) published by the Government of India fully tallies with the almanac. However, the traditional school also has its validity. Because Jyotish Shastra itself is not astronomy, and it is based on the words of Parashara, Garga, Mantreshwara who never used computers or western astronomy. Further, the planetary positions of Jyotish-nakshatra, rashi-or rahu, Ketu etc. depend more on belief and assumptions than science.
Read more about this topic: Vishuddha Siddhanta Panjika