Napier's Promptuary, invented by John Napier in the early 17th century, is a mathematical tool designed to simplify multiplication and division operations. It consists of rods marked with numbers, each subdivided into nine squares containing the products of the digits. To multiply two numbers, you align the rods corresponding to the digits of the multiplicand. Each rod shows the multiples of its digit, from 1 to 9. By reading the lines corresponding to the digits of the multiplier horizontally, you obtain partial products. The squares are divided into two triangles: the tens digit is placed at the top and the units digit at the bottom. By adding the numbers in the diagonally aligned triangles, you get the final result. This mechanism simplifies multiplication and division operations by reducing calculations to a series of simple additions. The Promptuary is not only effective for calculations but also a fun educational tool that can help children learn their multiplication tables, for example.

I recommend printing everything containing small numbers at 50% speed (Silent Mode).

Here is a video showing how to use Napier's Promptuary: https://www.napiermaths.com/napier-s-promptuary-youtube.html