Procurement is an important but neglected issue within the social science analysis of technology. Where studies have been conducted, they are typically marked by a schism between rationalist (e.g. economic) forms of analysis, where the assumption is that choice is the outcome of formal assessment, and cultural sociological approaches, which see choice as driven by the micro- politics of the organizational setting, interests, prevalent rhetorics, fads, etc.. While sympathetic to the latter critical view, we are dissatisfied with the relativist portrayal of technology selection: that decisions, beset with uncertainties and tensions, are divorced from formal decision making criteria. Influenced by Michel Callon’s writing on the ‘performativity’ of economic concepts and tools, we argue that formal assessment has a stronger relationship to technology decisions than suggested by cultural sociologists. We focus on a procurement that is characterized by high levels of organizational tension and where there is deep uncertainty about each of the solutions on offer. We show how the procurement team is able to arrive at a decision through laboriously constructing a ‘comparison’. That is, they attempt to drag the choice from the informal domain onto a more formal, accountable plane through the mobilization and performance of a number of ‘comparative measures’ and criteria. These measures constituted a stabilized form of accountability, which we describe through the metaphor of a ‘scaffolding’, erected in the course of the procurement. Our argument is twofold: first, we argue that comparisons are possible but that they require much effort, and second, that it is not the properties of the technology that determines choice but the way these properties were given form through the various comparative measures put in place.