Fig. 1.
Fig. 2.
Napier's Bones
From Napier Tercentenary Celebration Handbook
Napier’s rods or bones consist of ten oblong pieces of wood or other material with square ends. Each of the four faces of each rod contains multiples of one of the nine digits, and is similar to one of the slips just described, the first rod containing the multiples of 0, 1, 9, 8, the second of 0, 2, 9, 7, the third of 0, 3, 9, 6, the fourth of 0, 4, 9, 5, the fifth of 1, 2, 8, 7, the sixth of 1, 3, 8, 6, the seventh of 1, 4, 8, 5, the eighth of 2, 3, 7, 6, the ninth of 2, 4, 7, 5, and the tenth of 3, 4, 6, 5. Each rod, therefore, contains on two of its faces multiples of digits which are complementary to those on the other two faces; and the multiples of a digit and its complement are reversed in position. The arrangements of the numbers on the rods will be evident from [fig. 2], which represents the four faces of the fifth bar. The set of ten rods is thus equivalent to four sets of slips as described above.
From Drawings of Barbour Patent No. 130,404
It is unnecessary to go into the history of the Hopkins Bookkeeping Machine to show the evolution of the Art relative to this class of machines, as the features that have made such a machine practical were developed by Hopkins himself, and at the present date there is none to dispute the title since his is the only machine having the required combination referred to. The scheme used by Hopkins for multiplication in his billing machine is, as stated, direct multiplication or that of adding the multiples of digits directly to the accumulator numeral wheels instead of pumping it into the accumulator wheels by repeated addition of the digits as is more commonly used.