 Brews, this is what you wrote just above, 'In SI units, the meter is not expressed as the length of some physical thing, but as the distance light travels in a given time of 1/299*** seconds. Consequently, the speed of light becomes 299*** m/s by definition'.  So far that is absolutely fine with me, although words to that effect already appear in the article, but perhaps it could be made clearer.    You follow with this with (my emphasis), 'That opens the question of what can be done to determine the real speed of light?'.  What point are you trying to make here?   