This paper presents and discusses a fast and efficient method to study artefact-centric interactions in co-design sessions. The method is particularly useful for exploring the introduction of augmented reality (AR) environments since AR application representations combine both digital content and physical content, transforming the way users interact with the design object. Although protocol analysis is extensively used in cognitive studies of design, it is a time-consuming and cumbersome method and hence unsuitable for extensive analysis in industrial environments. Our real-time coding method makes it possible to perform “on-the-fly” coding of physical interactions in co-design sessions. Focusing on quantifying interaction occurrences, our results are consistent with those obtained with post-session coding. Internal validity was assessed using relevant statistical tests. Based on the data collected in co-design sessions we show how aggregate results, especially timelines and interaction densities, can be displayed rapidly at the end of each session. This research paves the way for a more general implementation of real-time coding of collaborative work sessions in industrial situations.