mains frequency indicator

例句：

1. 1. The main frequency indicator on the device indicates the device's power level.
   设备上的主要频率指示器显示设备的功率水平。
2. 2. The main frequency indicator on the radio is used to tune in to a specific station.
   收音机上的主要频率指示器用于调谐到特定电台。
3. 3.The main frequency indicator on the microwave oven shows the power level of the oven.
   微波炉上的主频率指示器显示微波炉的功率水平。