The design of controls and instruments affects how easily people can use them. A student project investigated this effect by asking 25 right-handed students to turn a knob (with their
right hand) that moved an indicator. 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 must be
turned counterclockwise). Each of the 25 students used both instruments in a random order.
The following table gives the times in seconds each subject took to move the indicator a fixed
distance. Note that smaller times are better.