British codebreakers called the teleprinter messages "Fish". The messages had been coded by an unknown German machine. They called the machine and its coded messages "Tunny". Colossus imitated the machine and read the coded message from a punched tape. It tried various possibilities of how two of the wheels had been set up. When Colossus found likely settings for two wheels, the codebreaker designed further programs for Colossus until likely settings of other wheels were found. Colossus did not perform all of the decoding process. It just found likely settings of the machine. The output from Colossus was then worked on by people who had a very good knowledge of the German language.