Depending on the magnetic field strength and the particular properties of the sample used, the same compound yields, often significantly, different NMR spectra. At the first sight, this discourages the simple visual comparison of NMR spectra and complicates the analysis of identical and structurally closely related molecules. This is due to the highly non-linear dependence between spectrum and the difference in the resonance frequencies (Δν) of the coupled nuclei (ΔΔν) relative to their coupling (J) (see Section 3.4 for a typical example). The socalled higher-order effects appear when |ΔΔν/J| becomes sufficiently small, usually <10. This behavior makes the observed spectrum often highly sensitive to the differences between the frequencies of the resonances (relative resonance frequencies). While the absolute resonance frequencies, Δν are dependent on the B0 magnetic field (NMR macroenvironment), the ratio of the resonance frequency relative to a reference signal (typically TMS), namely (Δν-Δνref)/Δνref, is independent of B0 and often referred to as the relative chemical shifts, Δδ, of the nuclei.