Freehand sketch is the most critical stage in the design process. The importance of the freehand sketch is in its ability to freely represent various projections of ambiguous drawing using a convenience tool, pen-and-paper. Recently, pen-based system which developed attempted to use pen as an input device, allowing sketches to be freely drawn on computers. However, as far as the various drawing projections, such as diagram, symbol, plan, elevation, section, perspective, etc., how are they interrelated to a designeris cognitive behaviour? Different media have different abilities to represent projections. Whatis the difference of design cognitive behaviour between conventional pen-and paper and pen-based system in view of both using a pen as a design medium? This research proceeds a think-aloud protocol analysis to present an analysis and discussion. Research results show that there is a relationship of gradual embodiment, mutually complementary, going from a whole to being dissected into sections between the different projections. Moreover, pen-based system is more than a pen, it allows designer to inspect a 3-D view during the sketching stage. This gives the designer more opportunities during the sketching stage to conduct the design thinking process based on the ambiguous 2-D projections and the more concrete 3-D images, as well as more opportunities for visual feedback