A motor-pump unit including an electric motor and a pump. A sliding slot is disposed at each of two corresponding sides of a screen of the flat display respectively, wherein the sliding members are installed in the sliding slots and movable along the sliding slots. The outside signal lines include a first portion, and a second portion that is higher in electric resistance than an electric resistance of the first portion, and the second portion has a bend. Mounted on a central axis within the inner space is a concentrically revolving rotor body. One of two measuring beams emerges from the probe at a fixed angle for measuring one of the compound surfaces, and the other measuring beam emerges from the probe at a variable angle for measuring a plurality of other compound surfaces.