From Ian Walker
Some years ago, a colleague and I helped someone with a similar problem to that of Hans-Peter Salzmann (22 February, p 36). At the time, she was using a sequential selection device known as Possum to write books and we devised a system based on Morse Code to speed letter selection.
The structure of the Morse alphabet assigns the shortest codes to the most frequently used letters, and appears to be an almost optimum solution. The ternary system used on mobile phones is a very frustrating input method as it is not letter-frequency optimised.
Newbury, Berkshire, UK
