This paper examines the study of computer-based performance monitoring (CBPM) in the workplace as an issue dominated by questions of ethics. Its central contention paper is that any investigation of ethical monitoring practice is inadequate if it simply applies best practice guidelines to any one context to indicate whether practice is, on balance, ethical or not. The broader social dynamics of access to procedural and distributive justice examined through a fine-grained approach to the study of workplace social relations, and workplace identity construction, are also important here. This has three implications, which are examined in the paper, and are as follows: First, that it is vital for any empirical investigation of the ethics of CBPM practice to take into account not only its compliance with pre-existing best practice guidelines, but also the social relations which pervade the context of its application. Second, that this necessitates a particular epistemological treatment of CBPM as something whose effects are measurable and identifiable, as well as something which has a socially constructed meaning and is tropic in nature. Third, that existing debates, against which this argument is set, which regard contrasting epistemologies and ontologies as incompatible, should be addressed, and an alternative introduced. Introducing situated knowledges (Haraway 1991)and material semiotic ontologies as such an alternative, the paper proceeds to analyse the ethics of a particular case of monitoring practice, Norco. Drawing on Marx (1998) the paper concludes that a fine-grain analysis of the social is vital if we are to understandfully the ethics of monitoring in the workplace.