Napier's bones are a mathematical tool invented by John Napier in the early 17th century to simplify calculations, particularly multiplication and division. They consist of a set of rods, each marked with numbers arranged in a specific way. When aligned correctly, these rods allow users to perform arithmetic operations by adding and reading off the results directly from the rods. The design of Napier's bones is based on the principles of logarithms, which Napier also developed. Each rod represents a digit and is divided into sections that correspond to multiples of that digit. This innovative device made complex calculations more accessible before the advent of calculators and computers.