Calculation of χ²(ΔW,ΔN) using the precession model and assuming that the time origin is a free parameter. We find that non-offset are possible and the smallest offset corresponds to the point ΔW ≈ 100 μas and ΔN ≈  +150 μas. At this point, the time origin is t_o ≈ 1998.45 which is ≈ 7 months too early.