Metrology & Measurement standard designed to inspect parallelism and flatness of slip gage blocks, measuring tools & other gauges by interference method.
Comes with calibration certificate & manual (in Russian) in original fitted plastic case.

Specifications:

• Diameter 60mm
  
• Thickness 21 mm (0.82 inch)
• Flatness of working surface 0.00007 mm (0.0000028 inch)
• Local deviations from flatness of the working surface 0.00002 mm (0.00000079 inch)
• Made in USSR - Lytkarino Optical Glass Factory

Flat glass is used to check for interference methods of measuring the flatness of plane surfaces 

of end measures of length gauges, measuring instruments and tools.