What a printed panchang holds
A yearly panchang lists the tithi, nakshatra, yoga and karana for every day with the times at which each begins and ends, the sunrise and sunset, the festivals and fasts, and the muhurtas for marriage, griha pravesha and other ceremonies. It adds the planetary positions, the eclipses of the year, the Sankranti moments and the lunar months with their adhika and kshaya months, and often the predictions for the year (the Varsha Phala) and the rashi-wise forecast.
Why two panchangs can differ
Panchangs follow one of two methods. Some are worked out from the old Surya Siddhanta and its tables (the Vakya panchangam of Tamil Nadu is a well known form of this), while most modern ones use the positions of the Sun and Moon found by modern astronomy, which is called Drik Ganita. The two can place a tithi or a Sankranti some minutes or even a day apart. The choice of place also matters, since sunrise and the tithi at sunrise depend on the city.
The same festival can therefore fall on different dates in different panchangs. Communities settle this by following the panchang of their own tradition, and the dates on this site follow Drik Ganita for the place chosen.
Some well known panchangs
Kalnirnay, published from Mumbai, is the most familiar Marathi almanac and is also printed in other languages. The Rashtriya Panchang is the national almanac of India, prepared from the Indian Astronomical Ephemeris and following the Saka calendar adopted by the Calendar Reform Committee in 1957. The Vishwa Panchang of Banaras Hindu University in Varanasi is a respected scholarly almanac of the north. Tamil Nadu, Kerala, Bengal, Odisha, Gujarat and other regions each have their own old panchangs and panjikas, often published by a family of astrologers or a temple for generations.