An electronic circuit has a clock input for receiving an input clock signal. A two-way communication system enables communication between a customer who is remote from the central monitoring station and an attendant at the central monitoring station. The alignment axes of the segments of second corrugations make an angle lying in the range 45\xb0 to 90\xb0 with the longitudinal axes of the first corrugations. The stored frequency data may include a difference between the recovered-clock frequency of the master port of the first device and a local-clock frequency of the multiport device. The control system is configured to send a signal to the brake actuator to allow gradient and speed dependent supplemental parking. The fitting assembly further includes a retractable end fitting having a housing, a tube extending within the housing, and a biasing member.