>One day the speed of light might be measured with a ruler and a clock. The next day, if the same measurement gave a different answer, no one could tell if the speed of light changed, the ruler length changed, or the clock ticking changed.

I guess that is why it is called "Special Theory of Relativity" and not the "Special Theory of Absolutes". :)

Actually, if the length of the ruler and and duration of the clock change at the same rate, the measurement of the speed of light would calulate to be the same in both frames of references.

[what is with these Mac keyboards. The repeat key action is way to sensitive. Every few letters appear doubled, and I have to go back remove the extra letters. Where is my PC when I need it.]