In engineering the student is often ‘faced with contrasting representations or models’ (Entwistle et al., 2005, p. 9), which Entwistle explores as ‘ways of thinking and practising’ (ibid). These contrasting representations are in electric circuits for example: graphs, mathematical models, drawings of circuits and the real circuits. In our research we have found that exploring the relationships - links - between these different representations, as well in the theory/model domain as in the object/event domain (Tiberghien, Vince, & Gaidioz, 2009) is of uttermost importance. We have developed a tool for investigation of ‘the learning of a complex concept’ (Carstensen & Bernhard, 2008a) which we have used in order to find critical aspects, which we call “key concepts” (Carstensen & Bernhard, 2008b), which open up the portal of understanding threshold concepts.

In this paper we will explore these links further. As we have continued our work on how students make links between the different islands of single concepts, in order to make a whole of the complex concept, we have noted that the links between these islands are of different kinds. We will here discuss what kinds of relationships these links consist of, and how they differ in ways of coping with them for students, and how the teachers may notice and highlight these relationships in their instructions.

We have video recorded students interactions during lab-work and analysed these tapes according to the Theory of Variation (Marton & Tsui, 2004). Now we are taking this further, and make a more detailed analysis of what the links are, and by that we contribute to the understanding of the nature of a threshold concept.