Andrew if you have a Spektrum system hooked up to the Pan module then you would check the box. Pan config screen should show Spektrum Valid. All other Radians that are down stream will show SBUS valid as the communication between them is SBUS as I remember. On the additional Radians (roll/tilt) the check box should be empty. Also depending on what Spektrum receiver you are using, if it is DSM2-1024 capable you would check that box on the Pan module. If you are on the Futaba system then the check boxes would all be empty. On the Pan screen you should see PPM Valid with the Futaba.