Spreadsheets are one of the most common end-user programming environments in use today, and their importance in the business world continues to grow. Although considered critical software tools in many industries, particularly the financial sector, it is now widely accepted that the reliability of end-user developed spreadsheets is very poor. In order to address this problem, recent research has focused on the design and development of tools to aid end-users in the testing and debugging of spreadsheets. But to design tools that complement end-users natural behaviour, a knowledge of their behaviour within the most common commercial spreadsheet environment (Excel) is required. This paper details the design and application of a novel, custom built, 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. The data acquisition tool was utilised in experiments to investigate deb...