A Time Zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time.
India's Time Zones were established in 1884. Originally there were two Time Zones, the Bombay Time and Calcutta Time. Bombay continued to have a different time (39 minutes behind IST) until 1955. IST, which is GMT plus 5.30 hrs, came into existence in 1905.
