[Florin_Andrei]

It's almost certainly all about the pattern.

I make telescope mirrors. The error I'm allowed is 100 nm. I would love to just drag my fingers over the glass and tell if something is not quite right with the optical surface. In reality, I need a pretty elaborate optical setup to amplify the errors about 1/2 million times, in order to see them.

I'm guessing the spatial frequency of the pattern in that experiment is on the same size scale like the vertical amplitude of it.

[taavi013]

It is rumoured that Bernhard Schmidt had so sensitive touch, that he could physically feel polishing results by his (only) left hand.

http://en.wikipedia.org/wiki/Bernhard_Schmidt#Mittweida_year...

[Florin_Andrei]

If this is about the early stages of polishing, I believe it (and I can do it myself).