Hmmm.....not quite sure what you are looking for and I do not know how to do what you are asking, but here are a couple of alternatives.
(i) Did you look at iStat menu's.
(ii) Browse to /System/Library/CoreServices and check out the WiFi Diagnostics application.
Hope it helps......
I've never seen signal strength shown as a percentage...not on a MBP, not on a phone. Your battery is quantifiable...it can be at 100% of capacity, 0% or anywhere in between. I'm not sure that signal strength can been quantified the same way. The meter you have now gives you an approximation of your signal strength. If you need to test how fast your connection is, there's plenty of ways to test that, but I don't know of a way to see it as a %.
If its giving you exactly the same info, why do you want to see it in numbers instead of bars? I'm just curious.
i know but id still like instead of full bars it show 100%, 3 bars 75%, 2 50%1 25% and of course 0 0%..
signal strength is usually in some sort of log format, with each increase/decrease being a 3db change. A better estimate would be
4 bars - 100%
3 bars - 50%
2 bars - 25%
1 bar - 12.5%
Also, what real difference does it make? A strong signal @ 4 bars, might be mostly noise and a weak clean signal @ 1 bar might work better.