The following Magnetic Anomaly Map was recorded over a firearm test site in the U.S. in 1995 by Geometrics Inc., to evaluate the effectiveness of the G-858 is detecting firearms, and to determine the typical detection thresholds of these common firearms. Several different types of firearms were tested together with ammunition, using a densely spaced survey (30cm line spacing) of magnetometer measurements.

The sensor was held 60cm above ground with data being recorded in continuous mode at a fast walking pace. The instrument sensitivity was selected to be 0.05 nT at 10Hz. This resulted in a measurement being made each 12cm, or approximately 11,000 discrete measurements. The total time to record all data was 34 minutes, once the survey grid was laid out. The data was then downloaded into a PC and plotted using the "Surfer for Windows" package.

Most of the firearms exhibit typical "magnetic dipole" characteristics with the magnetic "low" (in dark blue and pink) at the North end of the object and the "high" (red and yellow) at the South end. [However, #8 (30/30 rifle) and #2 (12 ga double barrel shotgun) show the polarisation to be quite different suggesting that they contain strong permanent magnetism with minimal induced effect.] There was no effort made to orient targets for a maximum and minimum signature.

Target # 4 (.357 revolver) is the smallest magnetic disturbance of the firearms and yet it is evident that its range of detection is at least 1.5m and possibly 1.8m to 2.0m. The ammunition anomalies at positions 1, 3 and 5 are much smaller and barely recognisable as targets of interest.

From the standpoints of detection and the re-location of identified targets, there is no reason why the 30cm line spacing is required. These data indicate something on the order of 60cm would be adequate which would reduce survey time by half. If however, there is sufficient time available, a closer line separation would always be preferred for small targets.