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Recent studies on the spatial grouping of the digits are reviewed with emphasis on six new experiments by the author. For several tasks including keyboard entry and telephone dialing, grouping by 3's and 4's is consistently best in speed. Differences in error rate are generally statistically insignificant. If successive numbers have different groupings (user cannot predict grouping), differences between groupings may not be found. Users often state preferences for larger groups than those producing best performance. The temporal grouping of the user's keystrokes reflects the spatial grouping on the source document; however, the number of digits keyed after each look or referral to a number is not necessarily an indication of optimum grouping. All data point to grouping by 3's and 4's as best.

The communication to which the present paper refers is the flow of information in and out of the human operator while he is performing a well-defined task. The steps in this process, the types of measures required in its analysis, and some recent data in human information processing are outlined. The paper ends with a brief evaluation of the function and the future of computer simulation in improving man-machine communications.

A method of scaling based on an iterative computer program is described. The program accepts as input any set of paired-comparison preference data and produces as output a one-dimensional scale of preference. The method is illustrated by application to actual data and the solution compared to that obtained by Thurstone's method on the same data. Finally, some remaining problems and present limitations of the method are described.