Notes. The models in this table correspond to purely isotropic Kriging. More elaborate formulas exist for correcting geometrical anisotropy through the rescaling or rotation of coordinate axes along the direction of major spatial continuity. In the above expressions, c₀ = lim_h→0 γ(h) is the so-called nugget constant that represents measurement errors or indicates a spatially discontinuous process. The quantities (c₀ + c) and a respectively represent the variogram sill and range. The pure nugget model corresponds to absence of spatial correlation.