[Eeglablist] Reference point location and Cleanline issue

[chester20080]

Hello all,
I am a postgraduate student in biomedical engineering and this is my first time analyzing EEG signals in eeglab. The recording is from a healthy person at resting state. The montage is based on the International 10-20 system and has 19 electrodes (no location file, the locations are automatically recognized with BESA 4shell dipfit). The recording was done with reference to point G2 set 1 cm under Cz at a sampling rate (frequency) of 256 Hz.

1) When I plot the spectrum I see two big peaks at 50Hz and 100Hz, while the 100Hz is higher than 50Hz. Is this harmonic power line interference? The problem is that the cleanline plugin does not remove this artifact at all, it does nothing, the interference remains at both frequencies unchanged, unattenuated.

2) The second problem is that I don't know how to use the information about the reference point G2 located 1cm under Cz. I have Cz coordinates in both polar and cartesian. "Under" means inside the brain vertically so Z coordinate needs to decrease by 10mm or does it mean externally following the spherical curvature of the head or something, in which case both X and Z change, but then it gets very complicated, what are the exact coordinates for G2? And then I have to create such a channel manually, insert the G2 coordinates and run re-reference? I'm lost.

Can you please help me? Thank you in advance.