Human computers and micro-observers were scientific workers who performed calculations or reduced and analysed data before the advent of electronic computers. They were a staple of big science during the 19th and early to mid 20th century. Despite their prevalence within big science their epistemic roles remain unexamined by philosophy of science. This paper investigates the epistemic roles of the human computers at the Harvard College Observatory 1880-1920 and of micro-observers at the Bristol Nuclear Research Group 1935-1955. This paper argues that the instrumentalisation of human computers and micro-observers has negative epistemic consequences for the methodology of science.