Editing Gridiron pendulum (section)

==Disadvantages==
Scientists in the 1800s found that the gridiron pendulum had disadvantages that made it unsuitable for the highest-precision clocks.<ref name="Matthys" /> The friction of the rods sliding in the holes in the frame caused the rods to adjust to temperature changes in a series of tiny jumps, rather than with a smooth motion. This caused the rate of the pendulum, and therefore the clock, to change suddenly with each jump. Later it was found that zinc is not very stable dimensionally; it is subject to [[creep (deformation)|creep]]. Therefore, another type of temperature-compensated pendulum, the [[pendulum#Mercury pendulum|mercury pendulum]] invented in 1721 by [[George Graham (clockmaker)|George Graham]], was used in the highest-precision clocks.<ref name="Glasgow" >{{cite book
  | last = Glasgow
  | first = David
  | title = Watch and Clock Making
  | publisher = Cassell and Co.
  | date = 1885
  | location = London
  | pages = 
  | url = https://archive.org/details/watchclockmaking00glas/page/288/mode/2up
  | doi = 
  | id = 
  | isbn = 
  | mr = 
  | zbl = 
  | jfm =}}</ref>{{rp|p.289}}<ref name="Matthys" />

By 1900, the highest-precision astronomical regulator clocks used pendulum rods of low thermal expansion materials such as [[invar]]<ref name="Britannica" /><ref name="Baker2011" /> and [[fused quartz]].<ref name="Matthys" />