Referring to: http://en.wikipedia.org/wiki/One-way_speed_of_light I am about to quote 2 sentences that obviously have different meanings. The problem is that I don't understand, why they have different meanings, and yet at the same time they appear to be understood as not negating each other: 1. "....they show that, when measured in an inertial frame, the one-way speed of light is independent of the motion of the source within the limits of experimental accuracy. In such experiments the clocks may be synchronized in any convenient way, since it is only a change of speed that is being measured..." (Under the heading: "Experiments that can be done on the one-way speed of light") 2."Although the average speed over a two-way path can be measured, the one-way speed in one direction or the other is undefined (and not simply unknown), unless one can define what is "the same time" in two different locations. To measure the time that the light has taken to travel from one place to another it is necessary to know the start and finish times as measured on the same time scale...." (Under the heading: "The one-way speed") So in quote no.1, they say that only the change in the speed of light is measured, and that is the reason for light speed being independent of the motion of the source? What does it mean? And if it is has nothing to do at all with the source, you may also say that a decisions to put a tank of water with 5 gold fish and not 8 gold fish, in the way of a light beam (the fish are always above the beam), is a human decision, independent of the motion of the source… so is that sentence, actually just playing with words? If so, why is this sentence included as part of the term "The one way speed of light"?