When two projectors are assembled in a stacked configuration (one on top of the other), the projector on top is called the "Commander", and the projector on
the bottom is called the "Receiver". When suspended from a ceiling, the projector on top is the receiver, and the projector on the bottom is the commander.
The commander controls the receiver, and the projectors are linked together. You can operate both projectors at the same time from the commander's control