Christensen and Bower (1996) and Christensen (1997, 2003) discuss disruptive innovation by applying Dosi's concept of disruptive technological trajectories (Dosi, 1982). In the studies on performance of hard disk drives, Christensen uses and re-uses “a reprinted graph," in which time and performance are on the horizontal and vertical axes. However, careful examination of different publications shows a varying shape and vertical axis, raising doubts about its reliability. In fact, whether the technological trajectories look disruptive or sustaining depends on the unit on the vertical axis. To present the nature of technological trajectories, it would appear more appropriate to set the vertical axis to volumetric recording density for hard disk drives. Moreover, the technological trajectories of hard disk drives would not be disruptive, if the vertical axis was adjusted to reflect weights of hard disk drives or amounts of their electricity use. It is conceivable that Christensen came to this conclusion that the technological trajectories are disruptive before considering a more appropriate performance measure for them.