It is actually 82 1/2 ° E. Time zones centered at intervals of 15° as difference of 1 hour translates to 15°; Earth rotates (Sun apparently moves) through a circle of 360° in 24hours. So it needs to be a multiple of 15°. In India's case the 15°norm can't serve because GMT+5 hours is 75°E falling in extreme west of the country, but central in Pakistan and so it is Pakistan standard time. GMT+6 hours (90°E) falls outside the bulk of Indian landmass, centrally in Bangladesh and hence is adapted as Bangla Standard Time.
Instead 82.5°E passing (near Allahabad) through the middle of the country longitudinally with almost equal stretches to east & west, is just right and so was selected for Indian Standard Time.
82°.5 = 75° + 7°.5 ~ 5hrs+1/2 hr.
Lack of awareness of local time can create problems at times as has happened with me. When I was trekking in lush green forests of lower Himalayan range in the state now known as Arunachal Pradesh, I was to return to my camp (on a peak, so can't be missed as it can be reached by just climbing). As I was used to IST and when I saw 05:00 PM on my watch I thought there was still one hour's daylight. But in the forest it became dark as night descended into a pitch dark dusk with trees densely packed making(with another companion)progress of my climb impossible.Groping, we climbed onto a horizontal branch of a tree - tired, hungry, thirsty (water was exhausted to the last drop), sweating turning to cold and even match-less. We had to wait for 4hours till a gibbous Moon rose flooding the hill with moonlight , to our shock we discovered that we were perched on a tree branch at about forty freet from ground. We reached our camp in ten minutes. That taught me the lesson that I should always reckon the 'local' time (40 miutes or about 92°.5E; ahead in this case).
Instead 82.5°E passing (near Allahabad) through the middle of the country longitudinally with almost equal stretches to east & west, is just right and so was selected for Indian Standard Time.
82°.5 = 75° + 7°.5 ~ 5hrs+1/2 hr.
Lack of awareness of local time can create problems at times as has happened with me. When I was trekking in lush green forests of lower Himalayan range in the state now known as Arunachal Pradesh, I was to return to my camp (on a peak, so can't be missed as it can be reached by just climbing). As I was used to IST and when I saw 05:00 PM on my watch I thought there was still one hour's daylight. But in the forest it became dark as night descended into a pitch dark dusk with trees densely packed making(with another companion)progress of my climb impossible.Groping, we climbed onto a horizontal branch of a tree - tired, hungry, thirsty (water was exhausted to the last drop), sweating turning to cold and even match-less. We had to wait for 4hours till a gibbous Moon rose flooding the hill with moonlight , to our shock we discovered that we were perched on a tree branch at about forty freet from ground. We reached our camp in ten minutes. That taught me the lesson that I should always reckon the 'local' time (40 miutes or about 92°.5E; ahead in this case).
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because it's a G like that