what India selected a standard model with an R-value of 82 degrees east
Answers
The Earth has been divided into 24 time zones of one hour each. Each of these zones covers 15 degrees of longitude.
As the local time differs by 4 minutes at every longitude, it would create a lot of confusion regarding time for any country as a whole which may stretch across several longitudes.
Therefore each country selects a central meridian and the local time of this meridian is the standard time of that country.
The local times which lie on different meridians are bound to differ.
The sun rises two hours earlier in Arunachal Pradesh as compared to Gujarat.
This causes a time lag of 2 hrs from Gujarat to Arunachal Pradesh to avoid confusion and to have a standard time for reference, The 82.30'Eastern Longitude has been taken as the standard time for the whole country.
The local time at this Meridian has been accepted as the Indian Standard Time (IST) throughout the country because it passes through the middle of the country.
It has helped to avoid a lot of confusion which would have been there by following different local times or in absence of a uniform time.