Slides for my talk at the Scientific Meeting at Centrum Wiskunde & Informatica, 29/05/2015 A standard procedure in humanities research is to evaluate the aptitude of a source by performing source criticism. This includes the examination of the validity, reliability and relevance of a source in the context of a given research task. By turning the physical manifestations of the sources into digital objects, the sources are transformed by the technology applied to them. Some of the used tools, such as OCR engines, do not yield error-free results. For humanities researchers, this means that they do not only have to deal with source-inherent biases, but they also have to take into account tool-induced bias. The aim of our research is to develop methods that enable humanities researchers to perform tool criticism by revealing uncertainty in the data by tracing tool-induced bias.