Latitudinal and longitudinal extent of the India is about 30°. As from Gujarat to Arunachal Pradesh, there is a time lag of two hours. Hence, time along the Standard Meridian of India (82°30'E) passing through Mirzapur (in Uttar Pradesh) is taken as the standard time for the whole country ,so that there is no time difference in India, It has been accepted as IST throughout the country to avoid confusion.

In 1905, this longitude was selected as the meridian to create the Indian Standard Time. In winter, the Indian Standard Time is 5 hours 30 minutes ahead of Greenwich Mean Time. In summer, this time difference is 4 hours and 30 minutes due to adjustments made for daylight savings time.The standard meridian of India is 82.5 degrees east of the Greenwich Meridian. This meridian passes through the city of Allahabad. It runs through the center of the country.
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