Thomas used the stepped drum principle of Leibniz. He also was the beneficiary of 150 years of growing industrialism - eliminating problems that had made the early machines so difficult to perfect. The stepped drum in Thomas Arithmometer was used in conjunction with a simple
system of counting gears and an automatic carry. The success of the machine was due to the many springs and other contrivances that destroyed the momentum of moving parts so they would not carry beyond their intended point - a frequent failing in earlier machines.