Determination of flatness from straightness measurements and characterization of the surface by four parameters

Since for medium and larger objects there is no usable flatness reference in the sub-micron range, flatness deviations must be found from straightness measurements. The extensive task o f coupling the straight reference lines into a reference f lat is done using a computer. This simplifies the measuring procedure and offers much statistical information. The method described can be seen as a generalization of the classical "Union Jack" method. Af ter evaluation, the measured surfaces are described by four independent characteristic parameters having an important practical meaning