Up to the present waypoint in this series on EM site magnetic fields, we have identified typical sources of time-varying magnetic field intensities, examined salient field characteristics and illustrated correct survey methods. Our goal this month is to analyze data collected at a proposed site and answer the key question of whether or not the candidate site is, as far as magnetic fields go, acceptable for EM use. In the process of analyzing the magnetic field survey data we will define some of the interpretive techniques involved and observe the distinction between localized (a.c. power) and non-localized (geomagnetic) time-varying fields. Finally, we will discuss the implications of EM susceptibility threshold vs. measured field ratios when considering remedial site shielding.