[ubuntu] How would I find the signal of my wireless router?

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http://ubuntuforums.org – I need to find the relationship between signal strength and distance from my router to my computer. I need a program that displays average signal strength and i will plot signal strength and distance on a graph. I'm running linux so i need a program that will give a signal percentage and not signal bars. What program can I use or mod to give me these #s (HowTos)