SIgnal strenght via router: get real value instead of 0

[andreapx]

I have a lot of devices that shows the signal as 0, but if I have a look at the map, 0 is the value between the device and the coordinator, while the connection with routers is good.
Is there a way to get the best connection of all the devices or the minimum of all the link that they passes using the best path?
Right now I can't say if some devices have really weak link or not.
Thanks!