Napier’s Bones were the forerunner of the slide rule, adding machine and calculator. They were invented by John Napier who was born in Scotland in 1550 and were based on the Gelosia method of multiplication, which had been introduced to Europe, from India, around 1200, by Fibonacci (The man with the rabbits and the famous number sequence). They were mainly used for multiplication and division although two other, more complicated, bones were added later to do other calculations.

I was undecided about whether to make a bone for zero and eventually decided that I would. Calculations can be done without a zero bone as you can just leave a space where it should be.

The last two photographs show how to do the calculation

76495 x 7

The numbers you don’t need have been blanked out on the last photo.

• Start at the right-hand side, on the row opposite 7. The last number is 5. This is the last digit in the answer.
• The next parallelogram has a 3 and a 3. Add these together to get 6 as the next digit (working from right to left)
• The next parallelogram has a 6 and an 8. Add these together to get 14. Write down the 4 as the next digit and carry the 1.
• The next parallelogram has a 2 and a 2. Add these together with the 1 carried from before, to get 5.
• The next parallelogram has a 4 and a 9. Add these together to get 13. Write down the 3 as the next digit and carry the 1.
• The final number is 4. Add it to the 1 that was carried, to give 5.
• The answer is 535465

The bones can be used to multiply much bigger numbers with several digits in each.