In this paper, a general compressing method is reviewed systematically a t first. Then the idea and steps of digging horizontally into the error hypersurface are presented, as well as an example. Since there exists serious and complex nonlinearity in the error hypersurface, training by gradient decsending techniques is often too slow when it is on a plateau and has the risk of trapping into local minima. Digging tunnels into the error hypersurface by means of rotation transformation will jump out of the plateau to speed up training or skip from local minima.