A resistivity meter passes an electric current through the ground and measuring the varying electrical resistance within the soil. Different resistances are linked to how much moisture the soil contains.
Features such as wall foundations, which drain well and do not retain water, will give a high resistance reading, whereas ditches and pits, which trap moisture, will give low readings.
It is one of the oldest, and simplest of the range of geo-prospection techniques available to archaeologists, but is also one of the most labour-intensive.
Resistivity is proving very successful at Yeavering, revealing in more detail the range of hall and sunken-featured buildings excavated by Hope-Taylor, but also offering new and tantalising hints of additional features, including areas of very high resistance, such as a metalled/paved areas for industrial activities at the entrances to the main enclosure.