  It was recently suggested -- based on general self-consistency arguments as
well as results from the bootstrap (arXiv:2005.07708, arXiv:2007.11539,
arXiv:2007.04190) -- that the CFT describing the $Q$-state Potts model is
logarithmic for generic values of $Q$, with rank-two Jordan blocks for $L_0$
and ${\mkern 1.5mu\overline{\mkern-1.5mu L\mkern-1.5mu}\mkern 1.5mu}_0$ in many
sectors of the theory. This is despite the well-known fact that the lattice
transfer matrix (or Hamiltonian) is diagonalizable in (arbitrary) finite size.
While the emergence of Jordan blocks only in the limit $L\to\infty$ is
perfectly possible conceptually, diagonalizability in finite size makes the
measurement of logarithmic couplings (whose values are analytically predicted
in arXiv:2007.11539, arXiv:2007.04190) very challenging. This problem is solved
in the present paper (which can be considered a companion to arXiv:2007.11539),
and the conjectured logarithmic structure of the CFT confirmed in detail by the
study of the lattice model and associated "emerging Jordan blocks."
