  The Chiral Magnetic Wave (CMW) [1] predicts a dependence of the positive and
negative particle elliptic flow on the event charge asymmetry. Such a
dependence has been observed by the STAR Collaboration [2]. However, it is
rather difficult to interpret the results of this measurement, as well as to
perform cross-experiment comparisons, due to the dependence of the observable
on experimental inefficiencies and the kinematic acceptance used to determine
the net asymmetry. We propose another observable that is free from these
deficiencies. It also provides possibilities for differential measurements
clarifying the interpretation of the results. We use this new observable to
study the effect of the local charge conservation that can mimic the effect of
the CMW in charge dependent flow measurements.
