Here a dislocation has been written at a small angle with respect to the vertical. Run briefly to let it relax to an equilibrium configuration. Over most of its length it is vertical, except near the center where it rapidly shifts from centered over one column of red atoms to centered over the next. We may think of dislocations at small angles as being made up of straight sections (pure edge or pure screw) alternating with kinks. How much shear stress is required to move the kink? If a kink were to move from the bottom of the crystal to the top, what would be the equivalent motion of the dislocation as a whole?