If you want to see the actual response of your monitor install this and plug in your calibrator and select current setting (default when it powers up) and then tools - verify calibration. A window pops up allowing various test charts to be selected. The default is suitable.
http://dispcalgui.hoech.net/
You will also need to install this and tell dispcal where it is
http://argyllcms.com/
You can also use this for calibration but might not want to. It currently doesn't support V4 ICC files. If that ever gets to be a problem I'd guess it will. Must admit I have only used it for verification against a profile it has installed but it should work as I have indicated.
Linux comes rather well equipped for judging monitors visually. Normally these images are separate so when viewing dark grey it may be best to cover the others up. They are also extreme particularly the botton of dark grey and the top end of light grey. All open source and down to KDE.
Might help. Top one should be easy. Steps should look even but dark and light ends of the others are likely to fade out in some cases. Mid grey is rather important.
John
-