It can be observed that starting from the third grid, which has only 26 grid points, the relative deviation is reliably below 10 -8 . Further improvement with increasing the grid size is slow and erratic. For the largest shifts in NiSAL, which occur at around 400 ppm, a relative deviation of 10 -8 corresponds to an error of around 4×10 -6 ppm, which is negligible. Hence, accurate finite field shifts can already be obtained with very moderate grid sizes. In the Supporting Information, we show that similar results are obtained when using REPULSION grids. On the right side of Figure , we show the relative absolute deviation of the 2nd order shifts from the finite field shifts, |δ 2nd -δ finite |/|δ finite |, as a function of the field strength (expressed as proton Larmor frequency). One can first observe that the deviation between the two approaches vanishes for small field strengths, which confirms the correctness of our derivation of the 2nd order approach and in particular of the sum-over-states equation for the τ tensor. Furthermore, one can see that the deviation has a linear appearance in the log-log plot, which means that it is a polynomial function of the proton Larmor frequency. One can observe that one order or magnitude change in the Larmor frequency (from 100 MHz to 1 GHz) corresponds to a four orders of magnitude increase in the relative absolute deviation of the 2nd order approach from the finite field approach. This observation is easily explained: When expanding the shift in powers of B 0 , odd powers vanish exactly because of symmetry.