The metal loading plate shall be flat and sufficient in dimensions to encompass the entire contact surface of the tyre under test, and with sufficient thickness to support the test loads described in 4.4 without visible deformation. The plate shall be made of a conductive corrosive-resistant metal, e.g. brass or stainless steel, and free from coating or obvious surface contamination, such as oxidation or corrosion. Aluminium shall not be used for the plate because of its high susceptibility to the rapid development of surface oxides, which may adversely affect reading accuracy.The loading fixture (see Figure 1) shall be capable of applying the tyre load to the metal in a radial direction, against the metal loading plate. Test load measurement accuracy shall be ±1% of the full scale.The sheet insulating material, such as polyethylene, PTFE (polytetrafluoroethylene) or equivalent, shall have sufficient strength to support the test loads described in 4.4 without visible deformation. The insulating material should have dimensions on all sides at least 50 mm greater than the metal loading plate. With insulating sheet installed between the metal loading plate and the loading apparatus base (see Figure 1), it is recommended that the electrical resistance between the plate and the loading apparatus be at least 1014Ω. In any case, the electrical resistance of the plate relative to loading apparatus shall be at least two orders of magnitude higher than the resistance of the tyre being measured.