By 1900, the highest-precision astronomical regulator clocks used pendulum rods of low thermal expansion materials such as invar and fused quartz.
bY 1900, ThE hIgheSt-prEciSiOn aStrOnoMical regulAtor cLoCkS useD Pendulum roDS of low theRmaL eXpanSiON MaTERIals sUCh as iNvAr And FuSed quArtz.