Indian Standard Time (IST) is the time observed throughout India, with a time offset of UTC+5:30. India does not observe daylight saving time, (DST) or other seasonal adjustments, although DST was used briefly during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971. In military and aviation time, IST is designated E* ("Echo-Star").
Indian Standard Time is calculated on the basis of 82.5° E longitude, which is just west of the town of Mirzapur, near Allahabad in the state of Uttar Pradesh. The longitude difference between Mirzapur and the United Kingdom's Royal Observatory at Greenwich translates to an exact time difference of 5 hours 30 minutes. Local time is calculated from a clock tower at the Allahabad Observatory (
) though the official time-keeping devices are entrusted to the National Physical Laboratory, in New Delhi.