The conventional theory of the synchronous machine is based on the assumption that the mutual inductances between the three direct-axis windings are all equal. The method is satisfactory for a calculation of the armature current, but the value of field current is considerably in error. Better results are obtained if another reactance is included in the equations to allow for additional coupling between the field and damper windings. The paper shows how the value of the additional reactance can be deduced from the short-circuit oscillograms.