This paper presents some details from an observational evaluation of a computer assisted detection tool in mammography. The use of the tool, its strengths and weaknesses, are documented and its impact on reader's 'professional vision' (Goodwin 1994) considered. The
paper suggests issues for the design, use and, importantly, evaluation of new technologies in
everyday medical work, pointing to general issues concerning trust – users’ perception of the dependability of the evidence generated by such tools and suggesting that evaluations require an emphasis on the complex issue of what technologies afford their users in everyday work
