Sitting at a table in a small conference room, research student Per-Ola Kristensson slides a stylus in a seemingly random zigzag across a grid of letters on a tablet computer. But words quickly appear in a space above the grid, often faster than he traces his stylus through the letters. And he traces a lot faster than someone could tap out letters or thumb-punch them on a Blackberry.

This may be the next major breakthrough in writing interfaces for small devices. Shark, or shorthand-aided rapid keyboarding, uses geometrical patterns to shape words, says IBM researcher Shumin Zhai. Users place the stylus on the first letter of the word and then keep the stylus in contact with the surface of the device as they move the stylus to touch the box for each subsequent letter.

The system recognizes most words quickly from the trace pattern, even though the stylus passes through many adjacent letters. These usually don't make sense as part of a word, but if the system fails to recognize the correct word, a dropdown menu offers a range of alternatives.

Zhai says most users can learn the Shark grid - designed with fast tracing in mind - in four training sessions and pick up speed as they memorise familiar word patterns and letter locations.

"Many people can do 50 to 85 words per minute in test," he says, which is about equal to an average touch typist and considerably faster than a mobile, Blackberry or tap screen - or writing by hand, for that matter, at only 10-20 words per minute.

The Shark system is currently only available for use on tablet PCs from www.alphaworks.ibm.com/tech/sharktext.