Locations due west are behind in time, locations in the east are ahead in time. For example, east coast USA is 5 hours behind me (British Summer Time) and Delhi is 4.5 hours ahead.
But here's where it breaks down. If I travel west to the USA, then keep going west, local time should get further and further behind BST. But what if I keep going west until I reach India? I should be a long way behind BST as I've been travelling west all the way. But India is actually
ahead of BST! It doesn't work
Round earth theory busted, yet again!