Abstract: A system 10 for measuring deflection and/or deformation of a layer in a pavement structure under load is disclosed and claimed. The system comprises at least one apparatus 11 including electric coils 17 sensitive to relative movement between them and a separately anchored body 18 of ferromagnetic material. The apparatus 11 comprises two longitudinally spaced relatively moveable discs 19, 22 and a body 21 of a resilient, transversely expandable material between the discs. A nut 25 serves to urge the discs 19, 22 towards one another thereby causing the body 21 transversely to expand to secure the apparatus at a predetermined depth against a wall in a test hole.