devention DEVO-7 User Manual page 18

4）Usage method
The tranning switch is above the left coner,named HOLD/TRN, see below:
When flying, if the trainer push forward the TRN switch, it means the trainer has
already transfer the operate control to the trainee. At the same time, the output data
displayed on the boot screen belong to the trainee's operate data. If the trainer push
back TRN switch, it means the trainer has recycle the operate control from the trainee
and the transmiter was operate by the trainer.
DEVO-7 Page 18 of 170