This article appeared in the Autumn 1969 (Issue #17) edition of the Kent Archaeological Review.
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No doubt many readers will be familiar with the broader aspects of resistivity surveying, though they may not have been directly involved with the actual measuring operations or the interpretation of the results. The latter usually involves much careful study and analysis before conclusions are drawn. Here is an opportunity to put your own deductive powers to the test.
Set out below is a pattern of readings taken at Springhead, covering an area approximately 75 feet square. The measurements were taken with a Martin Clark resistivity meter with a probe spacing of 5 feet, and 10 feet between the lines of the grid. The observations were made in good conditions in cultivated ground lying fallow between crops. The average reading for undisturbed ground may be taken as 27-32. All the original findings have been confirmed by subsequent excavation.
For the guidance of the less initiated it is generally reckoned that the readings will represent the type and condition of the ground up to a depth of one and a half times the probe spacing. Where the ground has not been disturbed the values do not vary appreciably though in some cases variations may be due to geological features not of human origin. This possibility may be ignored in the present case. Over a buried wall, floor or road, a value significantly higher than the average will usually be obtained. Conversely a filled up pit or ditch generally leads to a low value though this will depend on the nature of the filling.
There is indeed an identifiable feature within the area and the problem for the reader is to determine the nature and extent of the underlying structures be they pits, ditches, building foundations or roads. A detailed plan will appear in the next issue of the Review so you can check your findings.