How does a tautology say nothing?

In the Tractatus, Wittgenstein claims that tautologies 'say nothing'. Later he explains that when he had called tautologies 'senseless' he had had in mind the point that they possessed a zero quantity of sense. He holds that a tautology, insofar as it is the limit of a series of propositions of diminishing quantity of sense, constitutes a degenerate case of a proposition, somewhat as a point is a degenerate case of a circular conic section. But he also holds that a tautology resembles the result of a summing together of equal and opposite linear vector quantities. This essay makes a case for two main conclusions: first, that each of these models plays an important role in shaping the Tractatus's conception of a tautology as saying nothing in virtue of possessing a zero quantity of sense and, second, that the two models nonetheless remain unreconciled. The essay further argues that many of the puzzling features of the Tractatus's conception of logic arise from Wittgenstein's failure to bring about the needed reconciliation. These points are argued for by working through the development of Wittgenstein's views on these matters in the Wartime Notebooks and other pre-Tractatus writings.