Engineers at NASA Goddard Space Flight Center performed mirror metrology (ultra-high accuracy measurements) to ensure the Webb telescope mirrors fit perfectly.
Engineers at NASA Goddard Space Flight Center performed mirror metrology or ultra-high accuracy measurements – to a precision smaller than the width of a human hair – to ensure the James Webb Space Telescope mirrors fit perfectly onto the Telescope Structure. For more about the mirrors: https://www.nasa.gov/content/goddard/the-amazing-anatomy-of-james-webb-space-telescope-mirrors/#.VjkZpCuTLig Credit: NASA/Chris Gunn