Flatness is a basic geometrical quality ; since a plane is a simple element of the Cartesian system used in dimensional metrology, incorrect flatness measurements give rise to other related errors in form shape and, of course, even length.
In the intercomparison, the participants were requested to measure at PTB a single granite table of 1 m x 2 m with their own equipment and their own procedure.
The comparison measurements were all carried out in a temperature and humidity controlled laboratory; the granite table had an intentional flatness error of about 10 um to be determined. All participants contacted 104 points in a 100 mm x 100 mm grid. In the majority of cases the measurement results agreed to about 0.5 um to 1.0 um. On the contrary, the flatness deviation values determined by the different participants according to ISO DIS 8512 turned out to differ up to even a few um. A software intercomparison has been proposed as a means to explain these differences as a further step to harmonising the measuring methods.