Yeah, the "middle of the room buckle" is the worst. Logan849 is totally right about the tape measure. I learned that the hard way when I eyeballed it and ended up with a seam that looked like a speed bump in a living room. Had to pull everything up and start over. Now I'm the slowest tack strip installer on the planet, checking every gap three times. That one rush job cost me more time than ten careful ones.
My grandpa always said to measure the tack strip gap with a tape measure, not by eye. Rushing that step is how you get tension problems and those middle of the room buckles. Taking that extra minute saves a huge headache later.