QTR-Quadtone RIP

In the ink setup tab, can someone give me a layperson's explanation of 
what the density and limit selections do? 

I assume they deal with how much ink is applied, but that's just an 
assumption. 

I'd like to try creating an all-black ink curve for my epson 2400 
(turning of cyan, yellow, and magenta inks), and it would be good to 
know what density/limits do before I start tweeking. 

Best, David. 

PS - I've read the PDF manual for QTR that downloads with installation. 
It gave me some, but not really enough info. on density, limits, 
linearization, etc. to really understand what I'm doing. Are there 
other sources of info. I can check out, especially for someone just 
starting out in using RIP software?