The CCIR considering: a) that there are systems which handle graphic and alphanumeric pictures and transmit them by means of appropriate digital codes; b) that subjective tests often have to be used to assess the relative quality of the pictures and the effects produced on them by transmission errors; c) that methods for the subjective assessment of the quality of television pictures have been agreed (see Recommendation 500); d) that alphanumeric and graphic pictures have a specific character distinct from that of conventional television pictures, and the mental process involved in their subjective assessment may differ; e) that the results of subjective tests can be analysed and presented in many ways; f) that the results of subjective tests can be interpreted in many ways.