Napier Binary Multiplication Board

# Napier Binary Multiplication Board

1617 John Napier described three practical tools for doing math in his book "Rabdology".
One of them is a board that helps with the multiplication of binary numbers.
(This was well before Leibniz "officially" invented the binary system in 1676)

Here is a 3D printable version of the board, best used with with standard 16mm marbles.
It also somewhat works with grapes.

This version of the board consist of a 6 x 6 grid with numbers on the left, bottom and right margin.
At the bottom margin (below the numbers) there is an extra row used only for input.
At the right margin (beyond the numbers) there is an extra column to hold the second input number to multiply with.

### Properties of the board

The board has several interesting and also quite intuitive properties, concerning movement of grapes (or marbles) on the board.
- Imagine, we place a grape on the intersection of row 8 and column 4, this grape represents value 8*4 = 32
- Movin