Figure 2

Assembly of the step-stool function. Four consecutive steps (y_I to y_IV) in the assembly of a continuous function capable of describing sigmoidal and bi-linear growth profiles equally well. See Theory section for details. Coefficients are b₁ = 0.2, b₂ = 1.69, c₁ = 0.3, c₂ = 0.8, d₁ = d₂ = 50.