Spherical-against-spherical and flat-against-flat grinding can be self-truing, so in effect centuries-old clever results required clever testing to verify. Hig

Spherical-against-spherical and flat-against-flat grinding can be self-truing, so in effect centuries-old clever results required clever testing to verify. High tech in those days? Rumor I heard in the mid-1980s was that LLNL had [vertical?] lathes which could mechanically cut mirrors to optical-profile accuracy. Supposedly 100gpm liquid flows were required to keep the part temperatures uniform.