| 318 / | HD | ELECTRICITY: MOTIVE POWER SYSTEMS |
| 560 | DF | POSITIONAL SERVO SYSTEMS (E.G., SERVOMECHANISMS) {23} |
| 638 | DF | .~ With particular "error-detecting" means {13} |
| 652 | DF | .~.~ With particular position measuring instruments {7} |
| 663 | DF | .~.~.~ Potentiometer systems including autotransformers and Wheatstone bridges {4} |
| 667 | DF | .~.~.~.~ With a bridge in the feedback circuit {1} |
| 668 | | .~.~.~.~.~ Recalibrating systems |