On: In 1870, Lord Rayleigh used oil and water to calcu...

[qsdf38100]

Speed of light has recently been redefined, and is now _exactly_ 299792458 m/s. It’s no longer a measurement, it’s a definition.

[hollerith → qsdf38100]

That's a little misleading: either the meter or the second has been redefined to make c = 299792458 m/s.

[qsdf38100 → hollerith]

Since 1983, the meter is defined in terms of the distance traveled by light in a vacuum during 1 second, see https://en.wikipedia.org/wiki/Metre#Speed_of_light_definitio...

[ghkbrew → hollerith]

The second is (and has been) defined independent of length for a while. It's the time it takes for a certain number oscillations of a caesium atom.

The meter was redefined as the distance light travels in a specific time. So you could say that either the meter or the speed of light was redefined to make the speed of light a round constant, but not the second.