I have used one of these things. My friend, Paul Miller built three. It's an interesting tool. 

Here's a video of it in use.(not Paul's)

http://www.youtube.com/watch?v=2DCN2XHDx0g

For a look at what Paul does, check this out.

 

Wow! I had never seen one of these. Amazing control of the cut.

That's a particularly good video of one .

I saw St Roy using one once . He did a whole show describing it's use and let you have a sufficiently close video  inspection to empower  one to make one's own if one is sufficiently ingenious.

 

The idea behind the tool as St Roy described it is to allow the craftsman to produce several iterations of the same work ( early production) by stacking many layers of veneer to be cut in one pass.

 

This one in the video of built from a kit

here:

http://www.wpatrickedwards.com/EtudeMarq.htm