In a zigzag, the retracement of wave A by wave B will depend on the structure of wave B. For example, in Figure A.21, if wave B is a zigzag, it should retrace 0.5 to .786 of wave A. If wave B is a triangle, it should retrace .382 to 0.50 of wave A. If wave B is a flat, it should retrace at least .887 of wave A.