[Koshkin]

> we're slowly narrowing in on C in measurements

Interesting... I thought that c = 299,792,458 m/s exactly. So what are we are actually measuring here? The meter and/or the second?

[ekimekim]

I believe the OP meant that they're narrowing in on being confident that gravitational waves travel at C, not narrowing in on a more precise value of C.

That said, if we do obtain a more precise value of C, the definition that changes is the meter. The second is defined in terms of energy states of a caesium atom.

[Filligree]

Right you are. I wrote that a bit ambiguously.