  An interpretation of the charge dependent correlations sensitive to the
Chiral Magnetic Effect (CME) -- the separation of the electric charges along
the system magnetic field (across the reaction plane) -- is ambiguous due to a
possible large background (non-CME) effects. The background contribution is
proportional to the elliptic flow $v_2$; it is the largest in measurements
relative to the participant plane, and is smaller in measurements relative to
the flow plane determined by spectators, where the CME signal, on opposite, is
likely larger. In this note I discuss a possible strategy for corresponding
experimental measurements, and list and evaluate different assumptions related
to this approach.
