| 968 / | HD | HOROLOGY |
| 817 | DD | APPARATUS FOR PRODUCING PRESELECTED TIME INTERVALS FOR USE AS TIMING STANDARDS (generating clock signals for electric digital computers G06F 1/04; regulating frequency in general H03C, L) [G04F 5/00] {6} |
| 818 | DD | .~ Metronomes (periodic signalization by acoustic signals in general subclass 218) [G04F 5/02] {3} |
| 820 | | .~.~ Electronic metronomes (rhythm generation for electrophonic musical instruments G10H 1/36) [G04F 5/02C] |