A fringe-pattern analysing interferometer with a resolution of 1 10 -9 , stability of readings of about 0.1 nm, and an uncertainty owing to optical effects of less than 1 nm, has been used to study some systematic effects in gauge block length measurements. Measurements on steel and quartz plates with sub-nanometre reproducibility are reported. An accuracy of about 1 nm is demonstrated for a combination of reproducible wringing and slave-block techniques. The limitations of the present definition of the length of a gauge block are highlighted. A double-sided method for length measurement of gauge blocks has been realized, the results of which are not affected by excessive thickness of the wringing film and which incorporate a correction on the interferometer optics.

A primary-level comparator, with a reproducibility of 0.2 nm and intended for realization of a Systeme International length unit in the range of 1-100 mm, is reported. High-precision differential measurements of phase change on reflection from blocks and end plates are demonstrated. A set of experiments has been developed to measure systematic error associated with nonideal interferometer optics and deviations from flatness of an auxiliary plate. For specially selected high-grade 6-mm blocks, reproducible wringing has been achieved with a random uncertainty in length measurements of 0.1-0.2 nm. Subnanometer wear-off of the blocks as a result of the cleaning has been detected. Under the conditions of reproducible wringing, the accuracy of the length measurements is evaluated to be in the 2-3-nm range for 6-mm blocks.

A modern fringe-pattern-analyzing interferometer with a resolution of 1 x 10(-9) and without exclusion of systematic uncertainties owing to optic effects of less than 1 nm was used to test a new method of interferometric length measurement based on a combination of the reproducible wringing and slave-block techniques. Measurements without excessive wringing film error are demonstrated for blocks with nominal lengths of 2-6 mm and with high surface flatness. The uncertainty achieved for these blocks is less than 1 nm. Deformations of steel gauge blocks and reference platens, caused by wringing forces, are investigated, and the necessary conditions for reproducible wringing are outlined. A subnanometer uncertainty level in phase-change-correction measurements has been achieved for gauge blocks as long as 100 mm. Limitations on the accuracy standard method of interferometric length measurements and shortcomings of the present definition of the length of the material artifact are emphasized.

A new fringe-pattern analyzing interferometer, featuring ultimate resolution of a few parts in iOu, stability of readings of about 0. 1 nm and non-excluded systematic uncertainties due to optic effects of less than 1 nm, has been used to study some systematic effects in gauge block length measurements. Measurements on steel and quartz plates are analyzed. Limitations of the present definition of the length of the block are outlined. Stability and reproducibility of the wringing procedure for steel and quartz plates are reported. A new double-ended method in length measurements of gauge blocks has been realized.It includes determination of the corrections for non-ideal optics of the interferometer, curvature of the plate and deformations of the quartz plate due to wringing of the block to its surface. The result of the length measurement is not affected, in the first approximation, by deformation ofthe plate and the quality of wringing.