Bietti justified his approach by stating, “I thought it to be appropriate, in moderate cases (between 10 and 20 PD [prism diopters]) of A-V pattern to use a way, based on an entirely empirical concept, of weakening more than one part of the horizontal action, relative to the other one, in the same direction in which the insertion is shifted vertically”8(p582) (translated from the original Italian). He did not offer a mechanistic explanation as to why recessing the inferior pole of a medial rectus muscle would give more effect in downgaze than in upgaze. He did, however, cite Boeder20 as hypothesizing that there might be selective segmental innervation to the horizontal rectus muscles in upgaze or downgaze. According to this hypothesis, there might be increased active contraction of the inferior portion of the medial rectus in downgaze, and, hence, selectively recessing the inferior pole of that muscle's insertion would produce more weakening in downgaze. Boeder20 speculated about this, but he did not attempt to prove this concept. Although Bietti primarily justified his method on empirical grounds,8 subsequent investigators have tried to explain the approach on specific mechanical factors. Reviewing these articles reveals that they are based on either misquoting or misinterpreting the 1975 study by Scott.17 Ohba and Nakagawa quoted Scott as saying “ . . . horizontal muscle tensions are different between upper and lower margins of the muscle with different directions of gaze; i.e. horizontal tension at the upper margin is stronger than at the lower margin in the case of upward gaze.”12(p433) In fact, Scott said essentially the opposite. He wrote, “In 30 degrees upgaze the lower fibers stretch from 40 mm to 41.5 mm and the upper fibers relax from 40 mm to 37.1 mm which puts the entire strain on the lower fibers (more so if they are stiff).”17(pp186-187) This misquote was repeated by subsequent investigators.13 A 1990 study27 correctly cited Scott's findings but misinterpreted their implications. It properly reported the fact that the muscle fibers will shorten on the edge of a horizontal rectus muscle toward the direction the eye rotates, for example, superior fibers shorten on upgaze; however, the authors incorrectly interpreted that to mean that the shorter fibers were under greater tension. Subsequently, numerous other researchers10,14,22,25,28 repeated this same misinterpretation. In fact, muscle fibers that are passively shortened are under decreased tension. This is the basis for the weakening effect of an extraocular muscle recession or the force vector changes after transposition seen in Figure 2.