flow indicator

例句：

1. 1.The engineer used a flow indicator to monitor the water level in the river.
   工程师使用流量指示器来监测河流中的水位。
2. 2.The doctor advised the patient to use a flow indicator when changing positions during surgery.
   医生建议患者在手术期间改变体位时使用流量指示器。
3. 3. The flow indicator on the traffic light indicates when it is safe to cross the intersection.
   交通灯上的流量指示器表明何时可以安全过马路。