ΔE 7.8, close: similar, with a visible difference side by side. Rubber Black is a little lighter than Abaddon Black.
Can I use Rubber Black instead of Abaddon Black?
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Rubber Black is a little lighter than Abaddon Black.
Can I use Abaddon Black instead of Rubber Black?
The same difference applies the other way round: Abaddon Black is a little darker.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.