We study the space of all d-tuples unitaries u = ( 1 , … d ) using dilation theory and matrix ranges. Given two such v generating, respectively, C*-algebras A B, we seek minimal constant c that ≺ by which mean there exist faithful ∗-representations π : → B H ρ K with ⊆ for i, i is equal to compression P | H. This gives rise a metric D log max { } on set equivalence classes ∗-isomorphic tuples u...