  We discuss the forward-backward correlations of harmonic flow in Pb+Pb
collisions at the CERN Large Hadron Collider (LHC), applying standard multibin
measures, as well as proposed here new measures. We illustrate the methods with
hydrodynamic model simulations based on event-by-event initial conditions from
the wounded quark model with asymmetric rapidity emission profiles. Within the
model we examine independently the event-plane angle and the flow magnitude
decorrelations. We find specific hierarchy between various flow decorrelation
measures and confirm certain factorization relations. We find qualitative
agreement of the model and the data from the ATLAS and CMS Collaborations.
