DMSP/F2 and F4 precipitating electron data are used to determine statistically the systematic variations of the equatorward boundary with Kp as a function of local time. The boundaries were chosen by hand for every DMSP/F2 satellite pass in 1978. These in turn are used to assess an algorithm developed to choose the boundaries automatically. From the statistical variations each boundary is projected to a midnight boundary. The projected midnight boundary served as an index of auroral activity-the Auroral Boundary Index. Listing of the 1978 hand- and computer-chosen boundaries and the Auroral Boundary Index for 1978 are included in appendices.