Digital BW, The Print

Depending on the tool you are using to measure, there might be 
something better. Ernst made a post several weeks ago about Xrite's 
Colorport which allows making targets for several different 
measurement tools, and then measuring those printed targets. It's 
very much like MeasureTool, but it's FREE. A quick search of the 
archives, or the Xrite site would pull up the download link. And yes 
I do recall that it is PC and Mac friendly. It might be over kill for 
measuring a 21 step target, but it does allow for a few things like 
changing the observer color temp and angle. It will export to CSV and 
TAB and SPACE delimited text files with Lab, XYZ, spectral, and maybe 
one other I can't remember (density maybe?). It will also save a 
CGATS standard type measurement file (there's an example in one of my 
posts). It's worth the download if you device is supported.

Also, again depending on the measurement tool, you can get the same 
data from Xrite's ColorshopX, which does some spectral (per 
measurement)graphing, as well as 2D and 3D graphing of measured 
samples (Lab), and a bunch of other things including editing ICC 
profiles, and well more than I'll go into now. 14 day demo, $99 price 
directly from Xrite. It's been worth my $99 so far, but it might be 
more worthwhile to full color users, not that some of the tools 
aren't useful for B/W.

If you want I can give you a list of some of the common features I 
find useful, and maybe a few screen captures from Colorshop, I would 
say read the manual, and while it will give you a rough idea about 
the tools, it is not what I would call in-depth.