ΔE 6.9, close: similar, with a visible difference side by side. Russ. AF Grey Blue is a little darker than Grey-Blue 1920s-1930s.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Russ. AF Grey Blue is a little darker than Grey-Blue 1920s-1930s.
The same difference applies the other way round: Grey-Blue 1920s-1930s is a little lighter.
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.
See Grey-Blue 1920s-1930s on the colour wheel See Russ. AF Grey Blue on the colour wheel
All matches: Grey-Blue 1920s-1930s equivalents · Russ. AF Grey Blue equivalents