A multiple block adder is provided wherein carry select adder is used in the most significant bit block, a carry increment adder is used in the least significant bit block and a combination of carry increment adder and carry lookahead adder circuit is used in the middle block. The present invention is simple structured, not only can efficiently utilizes the movements of the rotation means in either way, but also can switch the rotation direction of the output shaft conveniently upon demand, with easy operations. When the handle is in a second position, the tension roller is retracted so that the belt may be removed more easily. The second masking plate has a second outer periphery corresponding to the first outer periphery, and at least one second cutout part corresponding to the first cutout part. The lenslenses isare formed on the single basemultiple bases to form the lens unitunits, using a die whose surface contacting the base slopes in relation to its central axis to allow the base to self-align. The first midplane connectors are arranged to connect to first circuit board modules, and are mounted over the first mounting locations on the first side.