A digital apparatus includes a timing control circuit, a period counter, a phase digitizer and a calculation circuit. More specifically, the present invention relates to a composition for preventing and treating metabolic syndrome, containing tanshinone derivatives that exhibit superior activity in enhancing metabolic activity, as an effective ingredient. The well-voltage select circuit adjusts the well bias on a power-switching transistor, and consequently protects the power-switching transistor from damage caused by gate breakdown and forwarding biasing of the well. The rod exchanging device is attached to the frame of the rod propelling device via a transverse mounting member. The perimeter sensor is located peripherally to the swimming pool and is capable of sensing the perimeter laser beam. The mount accommodates the electrical generation module and the electrical generator therein in order to have the electrical generation module and the electrical generator coupled between the seat and the frame.