Objects that are out of balance tend to want to be in balance. This is why an unbalanced object shakes when it is rotated. A car tire is an example. As the unbalanced tire rotates the heavy and light ends of the tire want to equalize their weight. Since the tire is a solid object the weight cannot move and the tire shakes as a result. Mower blades are the same way. To balance them you can either remove weight from one side of the axis or you can move weight as it relates to the axis. The Meg-Mo blades move the weight as it relates to the axis. To get an idea of how moving weight affects balance find yourself a yardstick. Balance the yardstick on your finger at 18 inches. The yardstick should sit perfectly level. Now if you move the yardstick either way even a quater inch the yardstick will start to lean in the direction that you moved it. Simple isn't it? Okay, now we know that unbalanced object shake as they attempt to balance them selves. We know that if you move weight you can either balance or unbalance an object. (At this point I suspect that a bunch of lights just came on) Now since the knives (blades) on Meg-Mo blades are able to move up and down as well as back and forth we are able to deduct (using our giant man brains) that, unless the knives are grossly out of balance, the Meg-Mo blades are able to balance them selves. Any questions?