beyond what has been said already since you didnt specify which clock you are talking about specifically there is also the special case of analog clock at train stations where the first second actually takes longer than all other.
This is because a train station typically has multiple clocks that should all show the same time and they archive this by having the seconds run a little bit too fast and then pause at the 12 position until the clock receives a sync signal and starts counting the next minute.
that makes it so all clocks are getting synchronized at every full minute so any variation could only happen within that minute and nobody will usually notice these.
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