| 356 / | HD | OPTICS: MEASURING AND TESTING |
| 928 | DD | INVESTIGATING OR ANALYZING MATERIALS BY THE USE OF OPTICAL MEANS, I.E., USING INFRA-RED, VISIBLE, OR ULTRA-VIOLET LIGHT (GO1N 21/00) {5} |
| 931 | DD | .~ Systems in which incident light is modified in accordance with the properties of material investigated (GO1N 21/17) {8} |
| 939 | DD | .~.~ Color; spectral properties, i,e., comparison of effect of material on the light at two or more different wavelengths or wavelength bands (GO1N 21/25) {4} |
| 943 | DD | .~.~.~ Using photo-electric detection (GO1N 21/27) {1} |
| 944 | | .~.~.~.~ For following a reaction, e.g., for determining photometrically a reaction rate (GO1N 21/27C) |