1 Department of Archaeology, Classics and Egyptology, University of Liverpool, 12-14 Abercromby Square, Liverpool, L69 7WZ, UK. t.elliot@liverpool.ac.uk.
2 Intelligent Ultrasound, Floor 6A, Hodge House, 114-116 St Mary Street, Cardiff, CF10 1DY, UK.
3 Department of Earth Sciences, South Parks Road, Oxford, OX1 3AN, UK.
4 Norris Scientific, PO Box 812, Kingston, TAS, 7050, Australia.