Abstract: A method for facilitating the determination of the thickness of a coating on an article, especially a highly elongate article such as a wire, having a ferromagnetic substrate for the coating, the coating being electrically conductive and of substantially lower magnetic permeability than the substrate, includes disposing in proximity to the article an inductively wound wire coil while applying an alternating electrical current to the coil. An electrical property of the coil is monitored for deriving a signal or other indication representative of the monitored property. The thickness of the coating may be determined from this indication. Apparatus for performing the method includes an inductively wound wire coil positionable in proximity to the article; a circuit for applying an AC current to the coil; and circuitry for monitoring the electrical property and deriving the signal or other indication.