[nitpick] That is to say, just as there is an objective (and not merely subjective) sense in which two rods can have the same length

Well, there are the effects of relativity to keep in mind, but if we specify an inertial frame of reference in advance and the rods aren't accelerating, we should be able to avoid those. ;) [/nitpick]

I'm joking, of course; I know what you meant.