| 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 | | .~ Metronomes (periodic signalization by acoustic signals in general subclass 218) [G04F 5/02] {3} |
| 819 | DD | .~.~> Mechanic metronomes [G04F 5/02B] |
| 820 | DD | .~.~> Electronic metronomes (rhythm generation for electrophonic musical instruments G10H 1/36) [G04F 5/02C] |
| 821 | DD | .~.~> Using electromechanical driving, e.g., of optical scanned recordings, etc. (electrophonic musical instruments in which tones are generated by electromechanical means, e.g., by using pickup means for reading recorded waves, etc. G10H 3/00) [G04F 5/02D] |