is the failure of the square law in V_gs for voltage dependence and the very poor modeling of V_ds drain voltage dependence provided by ?V_ds. Another failure of the equations that proves very significant is the inaccurate dependence upon the channel length L. A significant source of L-dependence stems from ?, as noted by Gray and Meyer, who also note that ? usually must be taken from experimental data.

Due to the wide variation of V_th even within a particular device number discrete versions are