A method for estimating a thickness related to multiple conductive structural elements of an object, the method includes estimating a height difference between an upper surface of a conductive structural element and an upper surface of a photoresists layer portion that surrounds the conductive structural element, to provide multiple height differences; estimating thicknesses of the multiple photoresists layer portions, based at least on the second part of the emitted radiation; and calculating thickness values related to the multiple conductive structural elements, wherein the calculating is based at least on the multiple height differences and on the estimated thickness of the multiple photoresists layer portions.