The Nepali Calendar
The calendar system in Nepal for measuring dates and the timing of seasonal festivals diverges from the Western Gregorian method (based on the earth's position around the sun) and the Asian lunar calender (following the phases of the moon). For over two millennia the Bikram Sambat system (BE) has been in effect in the region of Nepal and it is based on measuring the positions of the zodiac (prominent constellations in the night sky). This calendar still has 12 months and 365 days a year, but the beginning of the months are offset from the Gregorian months and the new year begins in mid-April. The months of the Bikram calendar are Baisakh, Jestha, Ashadh, Shrawan, Bhadra, Asoj, Kartik, Mangsir, Poush, Magh, Falgun,and Chaitra.
This ancient convention is rooted in the mystic tradition of astrology in the region. The masters of the art would track the positions of the planets among the constellations and interpret the implications on earthly matters. They could also establish the regular patterns and measure seasons accurately, but without the precision of modern optics and electronics equipment they didn't realize that the system had an slight error of just over 50 seconds ahead each year or one day every 70 years. After 2,060 years that offset has grown to almost 24 days, which begins to contradict the actual seasons that the calendar represents. Despite this realization, the societies that use the BE system have not yet implemented a correction. The Gregorian calendar does have to add an extra 24 hour day once every four years (eliminating years in multiples of 100, excepting years in multiples of 400), but "leap year" is an established pattern that remains successfully in effect, and the Gregorian system will have an error of one day every 3,500 years.