I have noticed that Brainstorm output for a scout as a relative plot was different from the output I obtain with Matlab by simply averaging the vertices. I have understood that this inconsistency was linked to the invasion of the sign of one vertex (1 out of 18). However, when this vertex was part of a smaller scout (just two vertices), the sign did not change. Hence, I think that the sign changed "relative" to the other vertices, but what is the criterion? how are the other vertices taken into account?

"We start by finding the dominant orientation of the scout, then flip the sign of the values that are not in the same direction (scalar product of the orientations < 0)."

The dominant orientation of the scout is obtained with SVD: