Main control panel
On some SEMs there is a key switch used to set the main power supply on or off.
Vacuum mode switch
Used to indicate High Vacuum (HV) or Low Vacuum (LV) mode. In LV mode the lamp is lit (on), when in HV mode the lamp is dim (off).
Specimen chamber vent
Specimen chamber evac
Used to indicate that evacuation of the specimen chamber and column is in progress (lamp is blinking) and when evacuation is complete (lamp lights up).