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Comment by monochromatic | Hacker News Reader

For small displacements, pendulums are already approximately isochronous.

One of the first definitions of the meter was a pendulum with a period of 1s afaik

Surely you mean 2 seconds?

  T = 2*pi*sqrt(L/g) = 2*pi*sqrt(1 m / 9.81 m/s^2) = 2.01 s

Hence pendulum clocks.