Re-referencing the active electrodes

[Francois]

@Beatrice

Just to make sure for another detail, If I want EXG5 (EMG) as a reference to A1 (EEG-ref) which is the reference to all the EEG electrodes should I just first create a process in the re-reference EEG option as EXG5 reference channel to sensor types or names A1. Then as a second step A1 as reference channel and sensor types or names EEG (all) ?

Keep the type of the EXG* channels as "EMG".
For display purposes, do not use the process "Re-reference EEG". Instead, create a re-referencing montage that you can edit freely and include, as I suggested previously:
https://neuroimage.usc.edu/brainstorm/Tutorials/MontageEditor

If you want the re-referencing to be used for further analysis steps that are not linear (ie. other than averaging, filtering, source estimation), use the process "Re-reference EEG" but only for the EEG.

For saving permanently the re-referenced values (ie. if you want to export the recordings outside of Brainstorm) or if you need to process the EMG signals, you could use the process "Standardize > Apply montage" with the montage you created previously for display.