| 968 / | HD | HOROLOGY |
| 837 | DD | APPARATUS FOR MEASURING UNKNOWN TIME INTERVALS BY ELECTROMECHANICAL MEANS [G04F 8/00] {4} |
| 840 | DD | .~ Using an electromechanical oscillator (subclasses 817 and 844 take precedence) [G04F 8/02] {2} |
| 841 | | .~.~ Using a piezoelectric oscillator [G04F 8/04] |