I just ran through the testing again, this time not setting anything for each of the 5-8 channels, progressively.
Of course if you don't link a control to a channel, the RF nags to make sure you really want to end calibrating after doing less than 8. This is generally fine. BUT:
Channel 6 MUST have a centering control linked to it! Not configuring CH 6 will result in inability to map ch1-4 to the correct controls in the main configuration screen, even if calibration appears to have worked!
In this testing, CH 7 was just fine not being used. But as hsamuels says, if you are going to assign something to it, it must be something with a center position.
Of course if you don't link a control to a channel, the RF nags to make sure you really want to end calibrating after doing less than 8. This is generally fine. BUT:
Channel 6 MUST have a centering control linked to it! Not configuring CH 6 will result in inability to map ch1-4 to the correct controls in the main configuration screen, even if calibration appears to have worked!
In this testing, CH 7 was just fine not being used. But as hsamuels says, if you are going to assign something to it, it must be something with a center position.