G stands for physics department.
0 1 indicates instrument division, measurement and test category.
N refers to testing or analyzing a small class of materials by determining their chemical or physical properties.
33/00 means that special methods not included in G0 1N 1/00 to G0 1N 3 1/00 are used to study or analyze large groups of materials.
33/569 represents a group of microorganisms, such as protozoa, bacteria and viruses.