The unit detects the spin balance through the MCU> If load is not balanced, the amperage vs the speed of the drum is out of wack. Don't forget motors on these have a tachometer that tells controller what the speed is, and also report amperage. The controller can detect motor amperage and as it attempts to go clockwise, then counter clockwise, then distribution mode then spin, it will read these values. If it is not what it should be, it will attempt to start again. I have found, once in a while, certain loads cannot be balanced. Best advice to customer is to make sure you run full loads, not small loads. The loads should also be of similar weight clothes. If you run a big bath towell and a few pillowcases, this may not be able to be properly balanced.