Five surfaces mutually orthogonal within 2 seconds of arc; precision tilt adjustment w/ leveling screws 120 threads/in.; matl fused quartz; surface quali type 80/50 per mil-o-13830; al coating, silicon monoxide overcoat; surfaces polished, flat to 1/10th wavelength; 1.5 in. Surface dimensions; base matl steel, gray enamel finish; hardwood carrying case
