ATM A question about Foucault testers

[Brandon Mathew <brandon@core.rose.hp.com>]

Howdy,

I'm to the figuring stage of an 8" F/6 mirror and have built a foucault
tester.  I've been taking measurements (not as easy as it seems!)  and
reducing the data.  But now I'm starting to wonder about how I've set up
the tester.  Should the numbers increase or decrease as the knife edge
gets further from the surface of the mirror?  My assumption is that they
should increase, but I notice that if I invert my data, it looks a whole
lot more like a tornado.  I just need a sanity check before I blow a huge
whole in the center of my mirror :-).

Brandon Mathew