  In future linear colliders the luminosity will depend on maintaining the
small emittance aspect ratio delivered by damping rings. Correction of
cross-plane coupling can be important in preventing dilution of the beam
emittance. In order to minimize the vertical emittance, especially for a flat
beam, it is necessary to remove all cross-plane (x-y) correlations. This paper
studies emittance measurement and correction for coupled beams in the presence
of realistic measurement errors. The results of simulations show that
reconstruction of the full 4x4 beam matrix can be misleading in the presence of
errors. We suggest more robust tuning procedures for minimizing linear
coupling.
