| 250 / | HD | RADIANT ENERGY |
| 200 | DF | PHOTOCELLS; CIRCUITS AND APPARATUS {11} |
| 201.1 | DF | .~ Photocell controls its own optical systems {8} |
| 203.1 | DF | .~.~ Following a target (e.g., a star or instrument pointer or other object) other than a pattern {2} |
| 203.3 | | .~.~.~ Self-luminous target {4} |
| 203.4 | DF | .~.~.~.~> Sun |
| 203.5 | DF | .~.~.~.~> Cathode-ray tube scanning |
| 203.6 | DF | .~.~.~.~> Airborne target, or spaceborne target other than the sun (e.g., star or missile) |
| 203.7 | DF | .~.~.~.~> With moving reticle in optical path |