This standard BS ISO 9344:2016 Microscopes. Graticules for eyepieces is classified in these ICS categories:
37.020 Optical equipment
This document specifies dimensions and permissible material defects and processing faults for graticules with diameters of 19 mm, 21 mm and 26 mm to be used in microscope eyepieces for the purposes of measurement, assessment and comparison.