variable-area recorder

例句：

1. 1. The variable-area recorder is used to measure the area of a moving object.
   可变面积记录仪用于测量移动物体的面积。
2. 2. The variable-area recorder was used to monitor the growth of crops in different regions.
   可变面积记录仪被用来监测不同地区的农作物生长情况。
3. 3. The variable-area recorder was used to collect data on air pollution levels in urban areas.
   可变面积记录仪被用来收集关于城市地区空气污染水平的数据。