Japanese Programmer/Artist Yamamiya Takashi created the above machine that represents a functional half-adder logic circuit. He was inspired after reading A. K. Dewdney's "A Tinkertoy Computer and Other Machinations". The operation in this circuit stems from Takashi's design of the AND gate. The AND gate's operation and look is seen inside his web page. At first, the half-adder design looks somewhat daunting, but it offers a certain aesthetic in puzzle-making and enjoyment in the art of logic. There is a piston-like wooden shape that represents the AND gate. The piston cannot move downward unless both L-shaped holders are also downward. This is logically equivalent to both inputs to the AND gate being 1. The downward extent of the piston is equivalent to an AND gate output of 1. This is a wonderful mechanical and artistic rendition of Boolean logic. As mentioned in the web page, the gears (3 of them) represent inverter functions. The rotating lever pinion at the top of the design is the 4th inverter. The pinions interact with the L-shaped racks to cause vertical motion, and vertical motion of the piston represents the AND gate outputs.