We investigate the technique of calculating ionospheric electric fields and currents and field-aligned currents using an equivalent current function obtained from a regional array of ground-based magnetometers at high latitudes (Scandinavian Magnetometer Array). Like similar calculations previously done on a global scale, the derived electric fields and currents are found to depend on the model of ionospheric conductivity assumed. Unlike the global scale calculations, the regional calculations are also dependent on the assumed boundary conditions. Additional information on the electric fields, currents, and/or conductivities is required, besides the ground magnetic variations, to obtain unique estimations of the ionospheric electrodynamic features. In the present case, ionospheric drift measurements from one of the Scandinavian Twin Auroral Radar Experiment radars help constrain the calculations. Analysis of an equivalent current function at 1835 UT on October 7, 1976, representing Harang discontinuity conditions, suggests that upward field-aligned current probably existed near the boundary between eastward and westward electrojets.