Dependence of the period of trapped sausage oscillations on the steepness index, α, for different wave numbers: k_x = 0.4 shown by the solid line, k_x = 0.7 shown by the dotted line, and k_x = 1.4 by the dashed line. The solid line stops where the oscillation becomes too leaky to accurately measure the period. For all the curves, the value of the parameter δ was fixed as 0.8. The period is measured in normalised units, equal to d/C_A∞, where d is the slab half-width and C_A∞ is the Alfvén speed outside the slab.