My first thought was that the pan was balanced on its center point, so one could solve it in two. Place the balls at the twelve points of the clock, note which

My first thought was that the pan was balanced on its center point, so one could solve it in two. Place the balls at the twelve points of the clock, note which way the balls rolled off (e.g., along the 3:00/9:00 axis), and then put those two balls and a normal ball at 12:00, 4:00 and 8:00 to see which way the pan tips and whether the abnormal ball falls off first (heavier) or last (lighter.) However, I see from these comments and the solution on the site that it's actually a scale with two pans so this method does not work.