Hi @RenataKoch,
The units for the Power cluster function will be [V²] for EEG, and [T²] for MEG.
Being x of the shape [nSensors, nSamples], the Power function returns the average across sensors of the square of the all the signals: mean(x.^2, 1)
GFP is computed as the standard deviation across sensors: std(x, 1, 1)
The results between power function and GFS.^2 are very similar or event identical as the mean of all the sensor values at a given time point is zero most of the time. If average reference is used, power and GFP.^2 are the same.