Deo-roll-on computer stylus

This is a small project that already dates back to 2009. I was in the first year of my undergraduate industrial design studies and we had a class with weekly changing topics. One task was to repurpose a simple product so that it would fulfil a new function and after quick ideation I decided to make sort of a digital stylus out of an empty deo-roll-on and a laser-mouse.

The laser simply tracks the backside of the ball and as a result you have a digital stylus. I had to exchange the mousebuttons with small pushbuttons, cut the PCB of the mouse in halves and connect the electrical tracks with wires, but in principle the electronics of the mouse were not altered.
I think the inspiration for this project were the mechanical computer mice of my childhood that worked by tracking the x/y rotation of a rubberized ball with the help of what I believe were two rotary encoders.