What is Indian standard time and what is its importance?

Time at any place in the world is calculated by the longitude of that place.

i. Indian Standard time or IST is a longitudinal line of 82.5 degree which passes through Mirzapur.

ii. The time is calculated in India according to this standard meridian and used by whole India as standard time.

In the west we have Gujarat and in the east, we have Arunachal Pradesh. The difference between longitudes of them is 30 degrees. 1 degree is equal to 4 minutes. If there was no IST, we would have a time difference of 2 hours between these two places. Therefore, we need Indian Standard Time.