[Thorrez]

Was the meter based on the length of the pendulum similar to the length of the meter today? This doesn't necessarily say they were similar:

> In 1675, Tito Livio Burattini suggested the term metre for a unit of length based on a pendulum length, but then it was discovered that the length of a seconds pendulum varies from place to place.

https://en.wikipedia.org/wiki/Metre#Pendulum_or_meridian

[petters]

The period is also not independent of the amplitude. That is only the case of you approximate sin x ≈ x in the differential equation

[madcaptenor]

My understanding (which could be wrong) is that actual clocks use a fancier pendulum than just a weight on the end of a string.

[purkka]

The difference in gravity around the Earth is small enough that the pendulums would be within a couple percent. (Wikipedia claims a measured difference of 0.3% from the time.)

Assuming the second was also quite accurate, the seconds pendulum wouldn't be too far from its current definition given that g ≈ π² to within ~1 % in modern units.