While the Gregorian calendar was embraced by the people of Britain, the National Calendar was embraced by the Maharajas of India. To put an end to his obsession with astrology, he produced a new calendar by using the exact same calendar, the solar calendar. The creation of the National Calendar marked the transition from the traditional solar Reckoning to the more routine National Calendars.
The National Calendar is based on the solar day/year cycle and not on the lunatic day/month cycle. The day/month cycle is considered to be approximate on the National Calendar dates. For example, a Hindu year lasts 365 days, while a Muslim year lasts 1000 days. Unlike the lunatic/solar calendar, which is embraced by almost all countries, the National Calendar is largely based upon the huge calendar and does not follow the lunar calendar. The National Calendar’s most widely utilized element, the moon, is not included in the calculation of the calendar year on which the beginning and end of every month are calculated.
Image Sources : nationaldaycalendar.com