@Damo *****
Not very well explained. Multi entry tourist visa gives you 60 days, then apply for 30 day extension = 90 days. Then border run and depending I believe which border you cross, possibly the Thai immigration take a dim view if you cross the border and return the same day. When you do get back into Thailand then you get another 60 day stamp, then apply for a 30 day extension, then another border run and same procedure for your final entry, 60 days + 30 day extension.