Another article. I have linked the previous article. This one from The Dreams of Tipu Sultan looks more complete.
The reforms introduced by Tipu Sultan in the prevalent Muslim calendar consisted of the following:
He reckoned the Muslim era not from the hijrat occurring in 622 but from the advent of Islam in 609 A.C. He chose to call this era ‘Maulud-i-Muhammad ‘ the era reckoned from the birth of Muhammad. Actually, however, his era begins not with the birth of the Prophet but with the proclamation of prophet-hood by Muhammad. In other words, his era begins thirteen years earlier than the hijrat.
Another measure adopted by Tipu Sultan in connection with the calendar was the adoption of the Hindu months and the sixty-year cycle. He, however, gave new names to the various Hindu months. Similarly each year in the 60-year cycle was given a distinct name. In designating the months and years, he made use of the abjad and abtath systems of evaluating every letter of the alphabet in terms of numbers. The abjad system which follows the ancient order of the alphabet had been quite common throughout the Muslim world for several centuries. In addition to this, however, Tipu Sultan employed another system of valuationknown as abtath in which the order of letters is the one that exists in the Arabic script. He also called it ‘^hisab-i-zar’
The numerical value of each letter according to the traditional Abjad system is as follows:
And the value of the various letters according to the Abtath is:
The names adopted for the months according to the Abjad and Abtath systems were:
Tipu Sultan also adopted the system of intercalary months. There was, however, a little difference between his system and the traditional Hindu system. Whereas these months were added by the Hindus towards the end of the year, Tipu Sultan added them in the beginning. The names given to each year in the 60 year cycle were as follows:
Also, it is worthwhile noting that like the Arabic script which is written from right to left, Tipu Sultan wrote figures also in this manner. Thus he wrote 54 as 45, 132 as 231, and 1217 as 7121.