Digital techniques in business industry have been greatly advanced. Among these, necessity for converting analog rotating value, shaft angle position, etc to digital has been increased as measurement for physical value and automation for control systems are advanced. Encoders, at present, have been widely used for factory automations, measurements, office automation devices, medical equipment, aviation and universal fields. Various kinds of encoders (FA-CODER® as trade mark) from small to high absolutional are available to meet all of the requirements. As a result of this, a maximum of resolution for encoder is one arc sec. High performance encoders supported by these high disk producing techniques are available.