CAUTION: A 6cm/2.4 inch” offset exists between the peak bar-graph and minimum depth measurement. This can be noticeable when locating shallow (less than 15cm/6” deep). The minimum depth reading aligns directly above the marker, rather than the peak response.

As the user moves the locator over the buried marker they see a peak in the bar-graph response which they use to locate where the marker is.

The red curve below shows how the peak is offset slightly from the true position of the marker. This is the same offset that we are talking about fixing with the offset to GNSS position measurements.

If the user switches their attention to the depth measurement displayed on the locator screen, they can look for a minimum depth measurement to locate the marker in a similar way.

The green curve shows how the depth measurement changes as the locator moves over the marker. The marker is directly underneath where the minimum depth measurement is. There is no offset using this technique. 

Its worth keeping in mind that the difference in position between the peak bar-graph and minimum depth will always be around 6cm.