Indian standard time is the uniform time calculated by the Standard Meridian of India. It is called as IST.
(i) India is a large country, almost 30 degrees are passing from westernmost state to easternmost state Arunachal Pradesh.
(ii) Due to that, here is a difference of two zones.
(iii) To avoid confusion or chaos for having different timings in different states of India, one standard meridian is taken to have a uniform time for the entire country.
(iv) Therefore, at 82°30'E has been taken as standard meridian of India which is almost passing from centre of India.