When multiple cameras are connected, select the camera to use for measurement.
In the item tab area, tap [Select camera].
Tap [Camera No.] [] and select the camera number.
If multiple cameras are connected, whether or not to capture images from each camera can be set. (FZ3-9/H9 only)
Reference
The image from the camera selected in [Select camera] will be the object to be measured in the following units. If you need to switch the camera during the process, insert a [Camera Switching] unit in the scene and switch the image. Camera Switching