One is the print from the computer and one where the feature we are looking at is marked. In common with the photographic prints there is a loss of quality attributable to the transfer process. The original plots are available for inspection during normal work hours at my office. Max -1 Contrast 1 Units Std. All plots are looking north to coincide with the photographs earlier.
Dark areas are high resistivity indicating the sandstone outcrop which surrounds the site.
High resistivity is the characteristic which we are looking for since hidden artefacts produce the same dark image. It is therefore necessary to process the data to remove natural high resistivity using computer filters. Low resistivity is demonstrated by lighter areas. These indicate an absence of background readings with ditches producing the lowest readings on a site and providing a good method of establishing man made ditch construction. Surprisingly there is an area of high resistivity shown in the central area of the fort, which looks like the clear outline of a building of some kind, even though there is absolutely no indication of anything on the surface.