A machine interface allows a user to select a machine operation. A plurality of questions are stored for output to a user. A score indicating the likelihood that the user will select a machine operation is stored for each corresponding machine operation. A next question for output to the user is selected from the stored questions by determining, for each of a plurality of the questions, an average of the least number of questions required to be answered by the user to arrive at each machine operation weighted by the respective scores, and selecting the question having the lowest average number. The selected question is output and an answer is received from the user. In response to the input answer a machine operation is carried out and/or the stored scores for each of the plurality of machine operations is adjusted. At least one further selection of a next question is then carried out for output to the user using the adjusted stored scores. A set of data determined from at least one input answer may be stored identified by a bookmark so that it can be retrieved when the bookmark identifier is determined from an input answer.