Two precision polygons, one with 24 and the other with 7 faces, will be circulated among the participants. Standard calibration methods using either one autocollimator and an index or measuring table or two autocollimators and a rotary table should preferably be applied. It is recommended to measure the polygons also in the reversed (upside down) position to detect optical asymmetry errors in conjunction with the autocollimator(s). Harmonic errors of the circular divisions can be derived from the results with the 24-faced polygon, whereas the 7-faced polygon can also reveal shortrange calibration and interpolation errors of the instruments. Additional interferometric measurements of the polygon face flatness will be performed by the PTB.
Optionally, only 12 faces of the 24-faced polygon can be measured.
*BNM-LNE will join the project at the end of 1997.