We review the Edwards transformation, and investigate the Robertson transformation and the Mansouri-Sexl (ms) transformation. It is shown that thems transformation is a generalization of the Robertson transformation, just as the Edwards transformation is a generalization of the Lorentz transformation. In other words, thems transformation differs from the Robertson transformation by a directional parameterq, just as is the case for the Edwards and Lorentz transformations. So thems transformation predicts the same observable effects as the Robertson transformation, just as the Edwards transformation does with the Lorentz transformation. This is to say that the directional parameterq representing the anisotropy of the one-way speed of light is not observable in any physical experiment. The observable difference between thems (Robertson) transformation(s) and the Lorentz transformation is caused by the anisotropy of the two-way speed of light. Therefore a physical test of thems transformation is a test of the two-way speed of light, but not of the one-way speed of light.