Institutional ethnography (IE) is used to examine transformations in a professional nurse's work associated with her engagement with a hospital's electronic health record (EHR) which is being updated to integrate professional caregiving and produce more efficient and effective health care. We review in the technical and scholarly literature the practices and promises of information technology and, especially of its applications in health care, finding useful the more critical and analytic perspectives. Among the latter, scholarship on the activities of economising is important to our inquiry into the actual activities that transform ‘things’ (in our case, nursing knowledge and action) into calculable information for objective and financially relevant decision‐making. Beginning with an excerpt of observational data, we explicate observed nurse‐patient interactions, discovering in them traces of institutional ruling relations that the nurse's activation of the EHR carries into the nursing setting. The EHR, we argue, materialises and generalises the ruling relations across institutionally located caregivers; its authorised information stabilises their knowing and acting, shaping health care towards a calculated effective and efficient form. Participating in the EHR's ruling practices, nurses adopt its ruling standpoint; a transformation that we conclude needs more careful analysis and debate.