ΔE 9.2, close: similar, with a visible difference side by side. Mechanicus Standard Grey is a little darker than RLM 72.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Mechanicus Standard Grey is a little darker than RLM 72.
The same difference applies the other way round: RLM 72 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 RLM 72 on the colour wheel See Mechanicus Standard Grey on the colour wheel
All matches: RLM 72 equivalents · Mechanicus Standard Grey equivalents