The specification of windows: ●GlassQuality Nd +/-0.0005 Vd +/-0.3% ●Diameter(mm) +0/-0.05 ●Center Thickness(mm)±0.02 ●Scratch-Dig 40-20 ●Power (fringe) 1 ●Irregularity (fringe) 0.5 ●Parallelism (arc min) 1 arc minute ●Bevels Upon requirement ●Coatings Upon requirement