  We completely classify Cartan subalgebras of dimension drop algebras with
coprime parameters. More generally, we classify Cartan subalgebras of arbitrary
stabilised dimension drop algebras that are non-degenerate in the sense that
the dimensions of their fibres in the endpoints are maximal. Conjugacy classes
by an automorphism are parametrised by certain congruence classes of matrices
over the natural numbers with prescribed row and column sums. In particular,
each dimension drop algebra admits only finitely many non-degenerate Cartan
subalgebras up to conjugacy. As a consequence of this parametrisation, we can
provide examples of subhomogeneous C*-algebras with exactly n Cartan
subalgebras up to conjugacy. Moreover, we show that in many dimension drop
algebras, Cartan subalgebras are conjugate if and only if their spectrum is
homeomorphic.
