The present invention relates to a front cover of target frames of dartboards with a tidy appearance and a long service life, which comprises a cylindrical housing frame provided with a flange at the bottom edge used for connection. The second axis of rotation is offset from the first axis of rotation, whereby the first three-dimensional shape and the second three-dimensional shape intersect to define a volume of intersection. This optical element is intended to direct some of the radiation emitted by the semiconductor body, which impinges directly on the reflective optical element, into an outer region of a target zone. The actuator is electromechanical and receives electrical drive signals to provide automatic flight control of the helicopter without requiring a hydraulic assistance system in the helicopter. A small diameter tube is fitted in a big diameter tube in the two adjacent tubes. Subtraction of the inverted from non-inverted water suppressed metabolite spectrum results in single or a combination of specific metabolite peakpeaks alone with a flat baseline for easier quantification.