title: Absolute figure measurements with a liquid-flat reference.
abstract: We describe a variation of the liquid-flat technique fordetermining the absolute flatness of a 240-mm-diameter optical surfaceto an accuracy better than 1/100lambda in both its horizontal(three-point support) and vertical orientations. Using theappropriate mathematics to calculate the surface deformation of a diskdue to gravity, we achieved verification of the method by comparingmeasurements carried out on a pair of optical flats and a liquidreference surface.
authors.forename: I
authors.initials: I
authors.lastname: Powell
authors.forename: E
authors.initials: E
authors.lastname: Goulet