four-ball apparatus

例句：

1. 1.The four-ball apparatus is used to measure the distance between two points on a map.
   四球装置用于测量地图上两点之间的距离。
2. 2. This four-ball apparatus can be used for measuring the angle of an object.
   这个四球装置可以用来测量物体的角度。
3. 3. The four-ball apparatus was invented by an inventor who wanted to improve the accuracy of his measurements.
   这个四球装置是由一位发明家发明的，他想要提高他的测量的准确性。