It is assumed that the reader is familiar with idea behind Yashid and the principle for the text-entering.
This mock-up is about the appearance of the device. No physical mock-up's has been made yet. Two ideas for actual devices will be presented in this paper.
A teenager is riding on a bus. She couldn't get a seat, so she's standing, maintaining balance using one hand. She receives a SMS-message and answer it with another SMS-message.
Frequent users of the SMS have already proven that they are willing to learn to enter text using a system that is a bit akward and which is limited by the speed of the users thumb-movement (in single-hand mode). Hopefully said users will be willing to endure a steeper learning-courve in order to use a system that is more efficient.
The most stable grip on a cell-phone would be an enclosing grip like the one used when hanging from a thin branch in a tree (association to pre-tech times intended). That grip - in a light version - makes it natural for all fingers, except the thumb, to squeeze or release whatever they're holding. In order to empower the thumb with good squeezing-possibilities, it can be aligned with the cell-phone (or the thin branch, to follow that analogy). This little thought-experiment gives us a close-to-natural layout of the buttons.
The display acquires at least 5 lines with 16 characters in order to provide an optimal reminder for the user. More lines gives better overview of the text, fewer than 5 lines will not work and fewer than 16 characters lowers the number of possible characters..
Yashid-on-a-stick could be used very much like the Twiddler. Their operate differently but they share their purpose.
The stick is very good for physical prototyping, since it can be coupled with a desktop computer for developing purposes (using the parallel-port or such) and potentially with a PDA for demonstration and context-aware tests. Since I have no idea how to modify an actual cell-phone to work with Yashid, the stick-design seems to be the way to go.
Toke Eskildsen, 27. march 2001