20 49 Right versus 4step ments affects how easily people can use them Timothy Sturm investigated this effect in a course project asking 25 right handed students to turn a knob with their right hands that moved an indicator by screw action There were two identical instruments one with a right hand thread the knob turns clockwise and the other with a left hand thread the knob turns counterclockwise Table 20 4 gives the times in sec onds each subject took to move the indicator a fixed distance RTLFT TABLE 20 4 Performance times seconds using right hand and left hand threads Right Subject Thread 1 113 2 105 3 130 4 101 5 138 6 118 7 87 8 116 9 75 10 96 11 122 12 103 13 116 Left Thread 137 105 133 108 115 170 103 145 78 107 84 148 147 Subject 14 15 16 17 18 19 20 21 22 23 24 25 Right Left Thread 107 118 103 111 104 111 89 78 100 89 85 88 Thread 87 166 146 123 135 112 93 76 116 78 101 123