The assumption that functionally rational notations can represent organisational spaces is central to engineering diagrammatical approaches in the delivery of advanced technology. This is reflected in a approach to notations which assumes objective, rationalistic ontologies. This form of rationalism in the modelling approach undermines notions of social context and social impact but, as such, has received little attention in the engineering literature to date. This paper opens the debate on research into notations and their relationship to sound method, suggesting that researchers need to rethink the ways in which the world is represented in engineering documentation. Empirical data from nine companies and 48 people involved in manufacturing systems projects is presented which provides evidence for this position.