How the hell did they measure clock speed if the passage of time itself is different?
...
"Dear tahw, over the past year, I have noticed something interesting in our correspondences -- more hours have passed on your end than mine, on average. I believe our clocks are ticking at different rate. Yours, phyzome"
(except measuring number of ticks, as communicated over fiber optics, and possibly with other tricks to cancel out communication lag)