NavList:

I ask this question of the list, after having looking into time divisions 24 hour day, 60 minute hour and 60 second minute but how the second was defined eludes me.   I have seen that a pendulum of 1 meter length has a period of a second so if that is how the second was defined I am ok with it.
Still I wonder if the definition of the second might have preceded the metric system defintions?

The problem as I see it is that  to have a clock of accuracy in the seconds, before electricity, quartz, and atomic, there had to be some way to decide how long a second should be.  Also there had to be some way to set ones instrument or clock so that the second reflect the divisions of the day with some reasonable accuracy.    I  dont have a problem with  variations in  the rate of  a clock  since that is easily compensated.

Longitude being the measurement affected particularly by variations in the length of the second and the number from uct.

So to recap, when was the second defined and when was it possible to create instruments that could count off seconds accurately?

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