Panchang is Hindu calendar based on position of the Moon with respect to the Sun. Panchang consists of five elements of time namely, Vara, Tithi, Nakshtra, Yoga and Karana. Mobile Panchang addresses Tithi and Vara elements. Tithi is time taken by the Moon to increase its angular distance from the Sun by 12 degrees. There are 30 Tithis in a lunar month, i.e. time Moon takes to complete a revolution around the Earth. When ecliptic longitude difference between the Sun and the Moon is zero degrees it is Amavasya Tithi and when this angle is 180 degrees it is Purnima Tithi. A Tithi on a Solar day is determined by calculating the ecliptic longitude difference between the Sun and the Moon at Sunrise at a give location on the Earth. Mobile Panchang uses sunrise time in Mumbai, India. This is same as Indian Standard Time.
One lunar revolution (lunation) is a month in Hindu Calendar and there are twelve months in a year except when a adhik (additional) month is added for synchronizing with the Solar cycle. There is a concept of Kshay month but it occurs rarely where as there is a fixed 19 year cycle for adhik month insertion. There are two conventions for mapping months on Tithis; one starts a month after new moon (Mobile Panchang calls this Marathi Panchang) and other starts a month after full moon (Mobile Panchang calls this Hindi Panchang).
Mobile Panchang enables easy navigation from Solar Year to a specific Lunar month-paksh-tithi. A list of major festivals with dates enables you to look up dates for Diwali and plan your celebration with a slide of a finger.