The Massey Plugins High Resolution Meter is a simple plug-in that comes within the free plug-in pack known as Massey Tools. A few other free utility plug-ins come in this pack as well, which isn't featured on Massey's main page anymore for whatever reason, but can still be found as a free download. I'd used these plug-ins before only recently did I get them on my system at home. You can find it on the old Massey website and all you have to do it download it and put the plug-ins in your plug-in folder. The whole process is quite simple and you should be able to have the plug-ins installed within a matter of minutes. You also literally don't need to know anything in order to use the High Resolution Meter, as it's simply a matter of viewing it in the proper way. It's a great meter because it shows a stereo feed for peak, peak hold, and RMS levels in a vibrant and easy to understanding metering system. There's no manual for this that I'm aware of, but one surely isn't needed anyway.
I've currently got the Massey Plugins High Resolution Meter plug-in on my system at home which is a Pro Tools 9 based DAW. I've got a Mac Book Pro with a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM, which I use to run Pro Tools 9 along with a Digi 002R audio interface. Being that you'll most likely just be using the High Resolution Meter on a master fader, I'd be shocked to hear if anyone had performance issues with it. I certainly have never had a problem with it.
While I may not be finding myself using the Massey Plugins High Resolution Meter on a daily basis, I do use it enough to recommend having it around for yourself. There's down side to having this and rest of the Massey Tools bundle on hand as they're good tools for your DAW regardless of how much you might be using them. This meter is the most accurate free meter that I've seen to date, so definitely do hesitate and go find it for yourself...