On Sat, 13 Mar 2010 20:55:17 +1100, "stu" no where just yet
wrote:

I've just posted a picture in http://www.metalworking.com/Dropbox called
"stusplate"(is it the done thing to put a direct link here?)
As you can see from the reflection of newpaper, the surface has a very fine
finish like no surface plate I have ever seen. It comes in a felt lined
lockable box. Does anyone have any idea what this sort of plate is?

Could be an optical flat. Your jpg doesn't show the size.
Inspection grade optical flats are typically 5 or 6" dia and
polished flat to within a fraction of the wavelength of green
light.

Jim