The research investigates how designers sketch specifically analysing the physical details of mark-making. It contrasts the physical representations with the abstract cognitive processes of architectural design. A new form of protocol analysis has been developed using video and computer records of designers' sketching activity. The research compares the designer's post-hoc commentary and interpretations of the sketching activity with the computer's record of that activity. This process will lead to a greater understanding of the relationships between ">design events and graphical events.