Put it in your dialer for detailed info. It used to be able to show real signal levels instead of bars once activated but now this is where we are. Need a little test kit to get the full info. May need to re-enter or reboot to exit the mode. Depends on the phone.
I’ve been in a lot of bad signal areas proposing repeaters or diagnosing issues and used it.
Actually, I would like to have an option to identify the cells devices are connected to.