measuring pixel gray values

I'm trying to measure the pixel gray value of a selected area. What I'm trying to do is to measure the average gray value of a selection. I'm trying to compare several areas of a gray picture to find out which one is the grayest (or darkest). Can Photoshop CS2 do this?

Blur... average. Also layer... new adjustment layer... threshold.

Also Histogram Palette Expanded view.
If you are going to be doing a lot of this for quantitative analysis, you might consider an upgrade to CS4 Extended.