Because they are awesome, Pat Ashforth, Steve Plummer and Ben Ashforth illustrate math through their crafting projects. Pictured above is their knitted version of Napier's Bones, a calculation device invented by Scottish mathematician John Napier (1550-1617). George Hart explains how they work:
The image below shows how to arrange the bones if you wanted to multiply by 76495. For example, the bottom row, labeled 9 at left, allows you to read off 9 x 76495. The rightmost digit of the answer is the 5 seen in the triangle at right. Then read off the remaining digits by adding the two numbers in each parallelogram, carrying as necessary, e.g., 1+4 gives 5 as the next digit and 6+8=14 gives 4 as the following digit, with a carry of 1 into the digit after that. The result can be quickly read off as 688455.
Crafters' Website -via Make