The contemporary IT society is relying on the development of computer technology. On the one hand,
computer technology is receiving help from the past wisdom of humankind. Typically we can simulate the
logical circuit of computer by using Boolean algebra without making physical circuit of logic. Boolean
algebra is the fused concept of logic and binary system. Because of periodical and technical background,
the computer abacus calculation of past and the computer of today have the differences of structural and
operational method. But the basic algorithm of their operation uses the same method. It is the complement
number. For example, there is no direct method to express a negative number with abacus calculation. It is
expressed by complement number. The complement number is used when big number is subtracted from
little number. The same way is applied even in the computer of today. In computer system, negative
number is expressed by complement number. Also the subtraction operation uses the same way. This
research has the intention to confirm the calculation method applied commonly to abacus and the computer.