What is the difference between vapour density and specific gravity with formula

Vapour density is the ratioo of density of vapour to that of hydrogen gas ormass of certain volume of any gas divided by mass of same volume of hydrogen.Vapour density= mass of n molecules of gas /mass of n molecules of hydrogen. whereas,Specific gravity is the ratio of density of a sub to the density of a reference substance . Specific gravity=debsity of given sub/denaity of reference substance.This is the main diff between specific gravity and vapour density in vapour density the reference sub is only hydrogen whereas in specific gravity it can be any thing (mainly water), also vapour density is of gas whereas specific gravity is of all solid, liquid, gas.