This paper sets out a new interpretation of the agency of scientific instruments in the field. It uses Actor Network Theory as a conceptual framework, which invokes the concept of non-human agency, meaning that scientific instruments can affect outcomes and processes. It argues that the instruments taken on expeditions by travellers on behalf of the Royal Geographical Society (RGS) had agency in knowledge creation simply by being present. Having bequeathed the instruments, the RGS had sanctioned the expedition, and knowledge had to result regardless of whether the instruments had been utilized as intended. The paper builds on the work of historians on the morality of precision, but, by engaging in a detailed comparison of rhetoric and action in two case studies, it suggests a different approach. Observing the strategies of the RGS for knowledge creation in varying circumstances, it argues that the instruments had agency owing to their embedded resource rather than their tangible numerical outputs. The instruments did not always work as mediators between humans and natural phenomena, as the human actants were not able to exploit them as such. Nevertheless, they had agency in knowledge creation as their presence ensured success. The paper is based on published and unpublished material, the latter in the RGS–Institute of British Geographers archives.