The B&C Spectrograph is mounted in the Cassegrain focal plane of the telescope at the offset guider box [L]. The guider box contains a guide probe [M] which deflects the light to a wide-field Erfle eyepiece [V] when the two-position, center-off toggle switch [U] for the Erfle flat mirror is momentarily switched into the out position. Movement in two coordinates is controlled by the motion toggle switch on the SCR control box [N]. In order for the beam to the spectrograph to be unobstructed, make sure that the guide probe is moved to one of the side limits of its travel.