We buy near end december 3 GMC-320. Just to see the result I remove the cover and let CG under the sun (not really violent in this season in France). 2 CG don't move (20/25CPM) but the third give 600CPM and go back to normal few minutes after. Without this solar exposition this last CG give coherent values with the others.
Did you have and idea of the problem ? How can I solve it ?