| 968 / | HD | HOROLOGY |
| 837 | DD | APPARATUS FOR MEASURING UNKNOWN TIME INTERVALS BY ELECTROMECHANICAL MEANS [G04F 8/00] {4} |
| 840 | | .~ Using an electromechanical oscillator (subclasses 817 and 844 take precedence) [G04F 8/02] {2} |
| 841 | DD | .~.~> Using a piezoelectric oscillator [G04F 8/04] |
| 842 | DD | .~.~> Using a magnetostrictive oscillator [G04F 8/06] |