A measuring apparatus includes a spectrum analysis unit having an input for receiving an input signal to be measured. Each of the stringers has a stop for preventing said slider from separating there from at each of its ends and the stringers are free to separate from closed position at the first end when a force is applied in a predefined direction adjacent to the first end. The running level model has a hierarchical structure with various running levels such as synchronously clocked levels, a user level for system exceptions, an event-controlled user level, a time-controlled user level, a sequential user level and a cyclical user level.