The measurement of conductance through a narrow channel interrupted by two controlled potential barriers has been reported recently. Reproducible periodic oscillations of the conductance as a function of the gate voltage were observed. By including the change in resonant levels with chemical potential the authors have used a tunnelling mechanism through localized changing levels in a modified Coulomb blockade model to explain this effect. In order to get rid of any unknown model parameters so as to justify the modified Coulomb blockade model, instead of the direct comparison of the period of conductance oscillations, they directly compare the box capacitances both from the calculation and from the value derived from the experiment.