The user issues commands to the control computer in three ways.
The choice of what to do next, or changing some parameter is done through the USER terminal. Every job, e.g. choosing a new set of coordinates, offsets , differential tracking rates and so on is broken down into a set of specific commands. The software which runs these screens is known as the User Interface or UI for short.
Lastly, there is a handset which controls the RA and Dec and the focus drive. The handset is on a detachable cord and can be plugged into the right hand end of the console or sockets on the telescope near the finder eyepiece. There is a second location on the telescope for the handset which is used in engineering mode. The two sockets are clearly marked. When observing, the handset must be plugged in to the "observer" station on the telescope. The Cassegrain instrument rotator is only controllable from push buttons on the telescope primary cell. You must release the mechanical clamp before rotation and re-clamp afterwards.