While QM can fully describe the NMR phenomenon, it is usually necessary to use a simplified model to keep the computations tractable. By using a small number of representative species (usually called spins, forming a spin system), it is possible to expediently compute an approximate spectrum with extremely good agreement with the observation using a limited number of transitions. However, due to the approximation it is usually necessary to apply a line width and shape to the transitions to prevent artefacts when constructing lines. Calculated spectra can be used for iterative data interpretation processes such as 1 H iterative Full Spin Analysis (HiFSA), which systematically varies the parameters used to obtain the calculated spectrum until it precisely matches the experimental spectrum. Now that the components of the spectrum have been defined, we can clearly define two related key terms: Resolution and Dispersion.