We have investigated how reliably an automatic direction-finder network manufactured by Lightning Location and Protection, Inc. (LLP), identifies cloud-to-ground (CG) flashes that effectively lower positive charge to ground (+CG flashes). To provide independent vertification of the occurrence of +CG flashes, we examined records from an extremely low frequency (ELF) system to determine whether 340+CG flashes detected by the LLP system had coincident ELF waveforms characteristic of +CG flashes. The fraction of +CG flashes that had coincident ELF waveforms increased from 0.67 for flashes with range-normalized amplitudes of 0--25 LLP units to an average of 0.93 for flashes with range-normalized amplitudes of at least 75 LLP units. We also analyzed ELF coincidence for -CG flashes recorded by video systems and by the LLP system. A comparison of the result for +CG flashes and CG flashes suggests (1) that false detection is negligible in the LLP system for +CG flashes with range-normalized amplitudes of at least 50 LLP units and (2) that no more than about 15% of the +CG flashes detected by the LLP system at smaller amplitudes are false detections. The true percentage of +CG flash detections that are false is probably even lower, because at least some of the decrease in ELF coincidence at low amplitudes appears to have been caused by an increase in the fraction of coincident ELF signals that occurred below the ELF system's noise level. ¿ American Geophysical Union 1989