The Full form of IST is Indian Standard Time. It is the time observed throughout India and Sri lanka with a time offset of UTC +5:30. India does not observe daylight saving time (DST) or other seasonal adjustments. In military and aviation time IST is designated E* (“Echo-Star”). Indian Standard Time (IST) is calculated on the basis of 82.5′ E longitude, in Mirzapur, Uttar Pradesh, which is nearly on the corresponding longitude reference line.