Some controls, such as scrollbars, compound the problem by forcing users to switch back and forth between fine and gross motor skills several times to complete an interaction (see Figure 19-1).

• 某些控件，比如滚动条，在交互时混合了这些问题。 强迫使用者在精细运动和粗略运动之间转换几次，才能完成一次交互（如图19-1所示）。