I can't read the tons of posts and replies about one-way light speed in this forum. I was criticised once for sustaining light speed should be equal in both outward and return trips and Einstein's method of syncing clocks as the only reasonable one. Then I studied some scientific articles gently suggested by somebody here and I became persuaded that nobody succeeded yet in measuring the one-way light speed. After that, someone else argued against the need of measuring the space and time in the round-trip of light that I claimed in a different thread. Finally, I went through the details of Roemer experiment. And I learned that in Roemer measure we deduce light speed from time increment that light from Jupiter satellite Io takes to travel the diameter of Earth orbit to reach observer's telescope. Thus, this appears to be a one-way or inward trip speed measure obtained from distance and retardation time. What I expect now is an ultimate and expert explanation of why Roemer's measure can't be viewed as a one way measure of light speed.