[ramshorns]

Four of the seven physical constants used to define the seven base SI units will change, so a bunch of physical constants that currently have exactly defined values will start being subject to measurement uncertainty. So μ_0 will no longer be exactly 4π × 10^-7 H/m, k_C = 1/4πε_0 will no longer be exactly 8,987,551,787.3681764 N m^2/C^2, and 1 mol of carbon-12 will no longer have a mass of exactly 12 g.

[Jyaif]

Why can't they update the Avogadro constant and keep having 1 mole weight 12g of carbon 12?

[spiralganglion]

And for that matter, isn't it a bit frivol to call it a constant, if it's based on something mutable? Perhaps "the Avogadro number" would be a more appropriate name.

[hluska]

I don't actually know what any of that means (this is either impostor syndrome or I'm just dumb), but it reminds me of why I love Hacker News so much.

Now to Google to figure out what the heck you just said...:)