Assertion: clock's pendulum | /r/HasProperty | operated in early 20th century
Facets:
value: often
type: TEMPORAL
Source sentences:
text: In the late 19th century and early 20th century, pendulums for precision regulator clocks in astronomical observatories were often operated in a chamber that had been pumped to a low pressure to reduce drag and make the pendulum's operation even more accurate by avoiding changes in atmospheric pressure.