To receive weak radio waves from the universe, the antenna surface needs to be extremely smooth, and the surface roughness is required about the same as the thickness of plastic food wrap. The roughness of the antenna surface is measured by using the method of radio holography and then adjusted in microns.
The picture shows the workers in the man lifts removing the holography receiver that was used to measure the surface accuracy in order to verify the receiver’s performance. As you can imagine, it is a daunting task to measure the surface accuracy of the large antenna dish (seven meters in diameter) with precision down to a micron. (Picture provided by Norikazu Mizuno)