The increasing complexity and demands of assembly operations in manufacturing has been shown to lead to increased cognitive load in assembly workers. Previous work has outlined the complexity of an assembly worker's situation both in terms of difficulty and speed of work and there have been a few attempts at creating frameworks and methods for understanding the key aspects of what creates increased cognitive load. This paper presents the development of an analytic method, denoted CLAM (Cognitive Load Assessment for Manufacturing), and a tool for assessing cognitive load in manufacturing, primarily assembly. It outlines the journey of the development as well as discusses and problematizes relevant meta-methodological issues paired with method development. The intended contribution of the work is to make a difference in reducing the cognitive load of assembly workers on the shop floor, thus focusing the development on applicability and usability of the tool in practice. With this purpose in mind, focus of the method development has been on the practitioners, i.e. the method should not require any expert knowledge to be applied. The CLAM method and accompanying documentation such as a handbook containing instructions towards using the method and interpreting the results, is available in an online tool.