Why is my AirPort RSSI a minus number?

Question

Just curious.  My RSSI reading is -80 - obtained by Optoin>Clicking the AirPort icon at the top of the screen.
How am I to interpret this number and why is it in minus territory?  Strong, weak?  What is optimal?  What is a good range?
Thanks to anyone who can lead me to this info.

Answer 1

Click on the Apple icon at the upper left corner of the screen.
Click About This Mac
Click More Info, then click System Report
Scan down until you see the Network heading, then click on Wi-Fi to highlight it
Look for the name of your current wireless network, then locate the listing for
Signal / Noise. Jot down the numbers that you see here, for example  
-50 dBm / -90 dBm
SNR = Signal minus Noise, so using the example below:
-50 dBm - (-90 dBm) = 40 dB SNR
Then use the familiar chart that was posted by expert user Tesserax to evaluate your signal quality.
o 40dB+ SNR =            Excellent signal
o 25dB to 40dB SNR = Very good signal
o 15dB to 25dB SNR = Low signal
o 10dB to 15dB SNR = Very low signal
o 5dB to 10dB SNR =   No signal
As you might imagine, the SNR will change in relation to the location of your Mac laptop to the router
You might also want to refer to the excellent User Tip that Tesserax has posted on this:
                 AirPort - Optimal Base Station Placement