This paper presents a detailed design of all mechanical and electronic parts of a Deviation Measuring Unit (DMU). This unit has been used as a feedback element for the horizontal part of a dual-axis sun tracker. The proposed dual-axis sun tracker is designed to be fixed over moving surfaces such as vehicles, trains or ships. The modeling, simulation and implementation of the proposed sun tracker was earlier introduced in a previous work. Due to the fast and discontinuous change of the relative sun direction in the horizontal plane, a need arose for having a feedback element with special specifications among the control process. The designed DMU proven to meet all the desired specifications and concerns to satisfy the special needs for the designed tracking control system.