The decorrelation of the second v_2 (left panel) and third v_3 (right panel) harmonic anisotropies between η_a and η_{-a} with the reference detector chosen at certain η_b ranges at 5-10%, measured by ATLAS (blue hollow box and blue solid box) and STAR (red solid box), and calculated with a (3+1)D ideal hydrodynamic model for LHC (blue solid lines) and RHIC (red solid lines) energies. The correlator r_n is calculated from the two-particle flow coefficients V_n∆ as: rn (ηa, ηb). The model describes the ATLAS 2.76TeV data and overestimate the effect at RHIC. With a viscosity correction with eta/s = 0.16 (magenta dash line) for RHIC, the results give a weak decorrelation for v_2 and an even stronger decorrelation for v_3.