Fig. 7. An example of how the exponential functions of the exponential model (Eq. [A1]) simulates the curvilinear part of the curve w_bs = f(W) of the vertisol (Eq. [16]), and how it can thus determine the effective beginning and end of variation of the curve. The mean deviations between the two fitted curves in the ranges {WD–WC} and {WB–WA} are 3.5 x 10^–4 and 1.4 x 10^–4 dm³ kg^–1, respectively.