As the locator is moved over the target, the waveform depicts the increase in the frequency of the locator's 20 Hz audio idling signal. The highest frequency occurs when the locator is directly over a vertical target, and over both ends of a horizontal target. The audio signal peaks over identical magnetic signatures at two joints of a cast-iron water line. Locating a survey marker in close proximity to a steel fence is no problem with the DML2000. Manhole covers normally appear as short horizontal dipoles with the peak signal level occurring at the perimeter of the manhole cover.
Frequency peaking occurs directly over service connections and valve boxes.