1. A method of determining the feasibility of a proposed structure analysis process, said process comprising electron beam excitation of x-rays from a multi-layered structure in order to determine the structure and composition of the layers, the method comprising:— i) generating predicted x-ray data representing the x-ray excitation response of the multi-layered structure according to a first set of one or more process conditions, using structure data defining the structure and composition of the layers; ii) analysing the effect upon the x-ray data of changes to the structure data in accordance with one or more predetermined feasibility criteria, wherein the said one or more predetermined feasibility criteria define whether or not it is possible for a structure solver, when given the x-ray data, to calculate output structure data defining the structure and composition of the multi-layered structure for x-ray data generated according to the first set of process conditions: and iii) automatically repeating steps (i) and (ii) using different process conditions in place of the first set of process conditions so as to determine under which process conditions, if any, the proposed structure analysis can be used to determine the structure.