The present invention is directed to novel polypeptides and to nucleic acid molecules encoding those polypeptides. The offset-nulling amplifier comprises a differential amplifier, an input stage for swapping the polarity of the input voltage at a periodic interval, and an output stage comprising a single-ended amplifier having an input switched at the periodic interval between the positive and negative outputs of the differential amplifier. The crown member has a mesa with a pattern exposing a portion of the plateau, and the mesa is smaller than the plateau. The couplers and the latching mechanism are located within the housings of the fixed and removable connectors to provide protection for the components from damage during storage, handling, transport and installation operations.