Napier's bones

Napier's Bones is a tool invented by the Scottish mathematician John Napier in the 1500s. It is made of strips of wood or metal with numbers and symbols on them. It is like a type of calculator where you can multiply or divide numbers very quickly. To use it you put the strips together in a certain way to form a square grid. Then you line up the numbers on each strip to make a new number, which is the answer. It is like a puzzle but the answer is a number, not a picture.