To measure a length accurately to within a millionth of an inch, we must have a measure graduated in millionths of an inch;a yardstick graduated in inches is useless.

• 为了准确测量一英寸的一百万分之一的长度，我们必须要有一英寸的一百万分之一的刻度，以英寸为单位的刻度尺是没用的。