A trigram table contains all possible three-letter combinations in a specific character set, for example ABC or LAR, along with the probability of each three-letter combination.
Trigram tables (in .trg files) are included with every installation of FORMS. Using the Lexical Analyzer , you can also create your own trigram tables for specific material. Start the Lexical Analyzer.
Specifying the location of trigram tables in Ehlocal.ini
Lexical Analyzer Help (this link will not work in Windows Vista, Windows 7, or Windows Server 2008)