To aid the development of spreadsheet debugging tools, a knowledge of end-users natural behaviour within the Excel environment would be advantageous. This paper details the design and application of a novel data acquisition tool, which can be used for the unobtrusive recording of end-users mouse, keyboard and Excel specific actions during the debugging of Excel spreadsheets. A debugging experiment was conducted using this data acquisition tool, and based on analysis of end-users performance and behaviour data, the authors developed a "spreadsheet cell coverage feedback" debugging tool. Results from the debugging experiment are presented in terms of enduser debugging performance and behaviour, and the outcomes of an evaluation experiment with the debugging tool are detailed.