[bad_user]

Simple. What's happening is that in the past we were measuring seconds relative to the duration of a day, but since then we've switched to atomic clocks.

So the day is not 24 hours or 86400 seconds, but rather 86400.002 seconds on average. That's about 2 milliseconds or more of deviation per day and for a whole year that's about 0.7 or 0.9 secs worth of deviation. Yet we still pretend that the day has precisely 24 hours, hence the need for leap seconds.

Given that since 40 years ago since leap seconds were adopted about 25 leap seconds have been scheduled, that sounds about right.