Digital BW, The Print

From my other posts you can see that I am trying to improve my knowledge of QTR.  
However, I also have a very basic question potentially applicable to a broader 
audience.  How can I use an Eye-One Photospectrometer to calculate density values.  I 
can see how to take a spot measurement of a patch and get an answer in a variety of 
colour spaces but how are these then converted to density values?

Thanks

Steve

PS:  do others have problems with the Eye-One rubbing along the surface of patch 
strips when using the strip ruler?