"The circle is important too. And the rook might not work so well for you, although you do have a pretty strong rook association so it's not completely hopeless. Still, being able to get usefully uniform harmonics in two minutes with a bag of glass pebbles and a rook is better than not being able to get them at all, isn't it? The geometric surface wouldn't be strictly necessary for this one as long as you had the pebbles laid out in a reasonably uniform circle with the rook in the center."