Like phunky says, the regular weave is 3 beats on each side. If you do an extra twist on one side, that will actually add one beat on each side which makes 4 beats per side (counting beats from both hands). The side that you didn't twist on gets an extra beat because it takes an extra beat to untwist. So an extra twist on both sides adds 2 beats per side. So in general, symmetric weaves will always have an odd number of beats.The same thing happens with the windmill except that the regular windmill is a 2 beat pattern, so symmetrical windmills will always have an even number of beats.