keytap technology to threatened languages, in particular N'ko; Gutowitz said he had eventually given up trying to get it supported by cellphone manufactures and begun to trial native language applications instead. Letterwise Design Unlike most if not all other predictive text entry systems, LetterWise does not depend on a work dictionary but is a prefix based predictive system. For each letter in the word the user taps the key associated with that letter on the keypad. If the letter chosen is the one required the user simply repeats the process for the next letter in the word, other Next is tapped until the required letter appears. It is claimed this is a very simple and efficient system to use, with no Multi-tap style time-outs or dictionary limitations. In an instruction manual it can be described in the following single sentence: "Hit the key with the letter you want, if it doesn't come up, hit Next until it does.". Letterwise is not designed to be eyes-free, that is the associated device display must be monitored to perform the next action. This contrasts to Multi-tap and some two key systems where some skilled and expert users are able to input using whilst not referring to the screen. Example Entering the word sirs which is a word with biases LetterWise strongly. A Multi-tap timeout will typically be one to two seconds wait for the cursor to move to the next letter but this can be interrupted by tapping the timeout kill or advance button (often down). A word such as mama would be more favourable to Multi-tap where 4 taps and no timeouts would be required; far less than the 14 taps and 1 timeout required for sirs. Software app versions Despite not included as a system keyboard, LetterWise was available in Email / Twitter / SMS / LiveJournal clients for Symbian, iOS as well as Qualcomm's BREW platform (distributed by the Verizon Wireless Get It Now service). Performance Performance figures for predictive text examples typically depend on use of natural language. Use of SMS language abbreviations and slang can reduce any advantage. For the tests done by Scott Mackenzie a selection of words from the British National Corpus were used as a representative sample of the English language. LetterWise uses the probability of letters occurring in a particular sequence to achieve performance. One measure of performance for text entry systems is "key