This measurement does not give the true energy, only compares the setpoint of the ninth dipole with that of the halla string. It only corresponds to the true beam energy if one has the beam going perfectly through the middle of the arc string with no energy shift. This is not currently the case. The BEM value (HALLA:p tiefen energy) takes into account this extra contribution and is probably closer to truth.
We have about -6e-4 of dp/p in the beam, so the true value is about 3352*6e-4=2 mev less than the mapper value.