In regards to mutual length contraction, Fig. 2-9 illustrates that the primed and unprimed frames are mutually rotated by a hyperbolic angle (analogous to ordinary angles in Euclidean geometry). Because of this rotation, the projection of a primed meter-stick onto the unprimed x -axis is foreshortened, while the projection of an unprimed meter-stick onto the primed x′-axis is likewise foreshortened.