  A vigorous defense of conventionality has been offered by Rynasiewicz (2012). He argues that his approach “has the merit of nailing the exact sense in which simultaneity is conventional. It is conventional in precisely the same sense in which the gauge freedom that arises in the general theory of relativity makes the choice between diffeomorphically related models conventional.” He begins by showing that any choice of a simultaneity relation is equivalent to a choice of a velocity in the equation for local time in H.A. Lorentz’s Versuch theory (Lorentz 1895). Then, beginning with Minkowski space with the standard Minkowski metric, he introduces a diffeomorphism in which each point is mapped to a point with the same spatial coordinates, but the temporal coordinate is that of a Lorentzian local time expressed in terms of the velocity as a parameter. This mapping is not an isometry, for the light cones are tilted, which corresponds to anisotropic light propagation. He proceeds to argue, using the hole argument (see, for example, Earman and Norton 1987) as an analogy, that this parametric freedom is just like the gauge freedom of general relativity.  As the tilting of the light cones, if projected into a single spatial dimension, would be equivalent to a choice of Reichenbach’s ε, it seems that Rynasiewicz’s argument is a generalization and more completely argued version of the argument given by Janis that is mentioned above in the third paragraph of Section 3.