Okay, a meter is the distance traveled by light in 1/299792458th of a second. It's relative, so the actual measure of a meter changes depending on your velocity (I won't even go into "Relative to what?", though I do sort of wonder if one could find a 0 point of velocity by measuring light going at equal speeds in all dimensions...). My point is there has to have been some point where we've used light to get an extremely accurate measure of a meter for whatever purpose. Now, where did they measure it, when, and in what direction were they facing the light? These things have a negligible effect on the matter, but it's still there...were they even taken into consideration, or is it akin to neglecting wind resistence in elementary physics problems? How big of a factor would the earth's angle and motion be?