In OS X Lion, I often used Wi-Fi diagnostics tool (screen, link) to report proper wifi signal level, since the wifi icon next to the clock in OS X menubar isn't reliable at all. (It shows full signal level even I'm too far from my router for internet connection to work...)
I can't find it in Mountain Lion. Is this functionality removed?
EDIT: Yes, the app is still there. The main screen looks slightly different though.