shell expansion indicator

例句：

1. 1. This indicator is used to measure the amount of gas that expands when a shell is heated.
   这个指标用于测量当壳加热时气体膨胀的量。
2. 2. The company uses this indicator to monitor the performance of its shell expansion system.
   该公司使用这个指标来监测其壳膨胀系统的运行性能。
3. 3. The engineers are using this indicator to detect any issues with the shell expansion process.
   工程师们正在使用这个指标来检测壳膨胀过程的任何问题。