Inversion of relative differences of the squared isothermal sound speed as a function of the normalised radius using various evolutionary models as references and targets for both 16CygA (left panel) and 16CygB (right panel). The inverted differences are compared in terms of the dimensional, u, and adimensional squared adiabatic sound speed, . The colours are associated with three different pairs of reference models and targets, all computed in Paper I. The continuous and dashed lines correspond to the actual differences between the target and reference models in adimensional and dimensional squared isothermal sound speed.