Eli5 : Why do we define metre as length of path of light in vaccum during a time interval of 1/299,792,458 of a second ?

Question

Why not 1/300,000,000 or something different constant ( why only light ) ?

In: Physics

Answer 1

Light moves at a constant speed so it’s good for measuring things precisely. The reason we don’t use a round number is because the meter existed before we had computers and that could measure in millionths of a second and we don’t want the meter to be longer than it used to be.