Napier's Bones Napero's sticks were described in a work published in 1617. They consist of ten rods numbered at the top from 0 to 9 and another rod called a ruler. This is my 3D printed version.
To carry out, for example, the multiplication between 10 and 5, sticks 1, and 0 are placed alongside the ruler.
You then choose the line corresponding to the number 5 on the ruler. To find the result, add diagonally, possibly with a carry; in our case we have the 0 alone (right), then the 5 and the zero (center) and finally another 0 (left). The result, therefore, will be 50.
Now let's do an operation with the carry. Multiplication between 9 and 815
Let's take the row of 9, write 7 - 2+0 - 9+4 - 5
7 - 2 - 13 - 5
<- carryover
7 - 3 - 3 - 5 the carryover (1) is added to 2
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