ABSTRACT
Mechanical ruling of diffraction gratings has roots going back to Fraunhofer [14.1] and, until technological developments in other fields made interference gratings practical (see Chapter 15), it was the only technique available. Its unique attributes guarantee an important role indefinitely. While the basic concepts are simple the extraordinary demands for accuracy have made the machines required one of the ultimate challenges in precision engineering. Starting again with Fraunhofer, who never described his machine, except to boast that "its performance could never be exceeded by hand of man", there has been an aura of mystery surrounding these machines. Many of their designers and builders worked so hard and for so long that they became reluctant to disclose more than a general description, and sometimes not even that.
