[lxgr]

Only if you disregard observers in different frames of reference interacting with each other, which you shouldn't when you need high precision and it comes to projects spanning Earth, Earth orbit, and the Moon.

GPS wouldn't work without accounting for relativity, for example.

[kijin]

You're missing the joke. It's still one second per second, only that everyone's second looks different.

[layer8]

Exactly.

[lxgr]

Yeah, I guess I don't see what's funny about that statement.

Unlike "sometimes a second is longer than a second" (not literally true but it makes some sense in the context of relativity), this one just seems like a tautology to me.

[kijin]

Yeah, it might not be funny, but the tautology draws attention to the fact that there is no privileged frame of reference.

In other words, the only thing we can say without qualification is that a second is just a second in the same frame of reference. All other statements must be heavily qualified.

Even things like "A's second is longer than B's" are only valid in some frames of reference and not others.