Link Quality, Signal Level, and Noise Level

Hi,

Cheers!

I know I should be asking Jean Tourrilhes about this but I know someone
here knows the answer to this "basic" question :b.  iwlist eth1 scanning
shows the following messages:

eth1      Scan completed :
          Cell 01 - Address: 00:0C:41:14:02:EB
                    ESSID:"eazix"
                    Mode:Master
                    Encryption key:on
                    Frequency:2.412GHz
                    Quality:242/0  Signal level:-78 dBm  Noise level:-64
dBm

I want to ask what the last line indicates.  
	For QUALITY:
		What is the "best" Link Quality Value?
		What is the unit of the Link Quality?
		What does 242/0 mean (can't get what the /0 mean)?
	For SIGNAL LEVEL & NOISE LEVEL:
		What is the "best" Signal Level and "worst" Noise Level?
		Which is a better Signal Level: 78 dBm or -78dBm?
		The previous question tries to point out if a large
negative value is good or bad?
		
I am asking this because these values are part of my heuristics in
connecting in a multi-BSS/IBSS environment.


Thank you very much.

Best Regards,
Rodel Miguel