You mean in like meters? > Each observatory has two light storage arms that are 4 kilometers in length. [...] A passing gravitational wave will slightly stretc

You mean in like meters? > Each observatory has two light storage arms that are 4 kilometers in length. [...] A passing gravitational wave will slightly stretch one arm as it shortens the other. [...] Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10⁻¹⁸ m. With the nominal hair value being 75 µm, `apt install qalc` tells me that's > 75 µm / 10^-18 m (75 * micrometer) / ((10^-18) * meter) = 7.5E13 so a change in length 7'500'000'000'000 times smaller than the width of a hair https://en.wikipedia.org/wiki/Gravitational_wave https://en.wikipedia.org/wiki/Gravitational_wave , https://en.wikipedia.org/wiki/Hair%27s_breadth https://en.wikipedia.org/wiki/Hair%27s_breadth