The addition blank served as the material for this test also. Each column of 10 digits was regarded as a unit, as if it were the only material on the page. Each and every combination of two successive numbers which, when added together, equaled 11, were to be canceled by drawing a line through them connecting the two.3 Thus the combinations found would be: 2 and 9; 3 and 8; 4 and 7; 5 and 6; and the same in their reverse order. A group of numbers, such as 4, 7, 4, would be regarded as two such combinations and a line drawn through, connecting the three digits. Figure 20 shows a portion of a number cancellation record. The frequency of combinations of two successive digits equaling 11 is of course not the same in all blocks of digits, but as the 5-minute interval allowed for this test was sufficient for most of the subjects to cover several blocks of the material, this factor was neglected. The subjects were instructed to go over all the horizontal lines of the 8 blocks of material on the blank and to check each one of the desired combinations. Then the vertical columns were checked, beginning as before at the upper left-hand corner. Previous to each trial it was impressed upon the subjects that they must mark every combination equaling 11 and that they would be penalized for leaving unmarked any such combination in the material which they had gone over. Immediately at the end of the 5-minute interval allowed for this task, the blanks were taken up. In scoring the record the last combination mark was considered the limit of the material which they had covered.