But what neither Brews nor yourself have been willing to tell us is: "what is this real speed of light?" Can we measure it? The measurement of the speed of light (as we all seem to have agreed on its definition) presents no problem at all, so long as you can provide a length standard that is sufficiently precise. The speed of light is still measured, at inner solar system scales at least, and to admirable precision. All of this after 1983.  (talk)