In the seventeenth century, John Napier invented a method to perform multiplication using small rectangular pieces of bone labeled with numbers. Select a digit and a number with at most four digits; to multiply them, put the columns with each digit of at the top of the columns after the first. Each column consists of multiples of those top numbers by , with digits placed in the corners of the squares. Go down the first column to the digit . Look at the red rectangle to its right; to get the answer, add the digits between the diagonals as shown by the arrows.