Excuse me, if i posted on a wrong forum. I heard this quite a time ago, that one day on Earth is not exactly 24 hours. And i'm pretty sure some unit charts on the back of composition books will say one day is 23.9 hours or something like that. My fantasy about how we defined the length of a day is that, in the first place, somebody divided the length of a day as exactly 24 hours, then made smaller divisions with minutes and seconds. I assume the rotational speed would not change the 60 seconds-60 minutes-24 hours scheme. In case of analog clocks, we can tweak it so that the hands move just a little bit faster to make them look like it always takes exactly 24 hours for a day. For digital clocks, it may be more "accurate" to tweak it so that at 24th hour, the day ends at 56 min and 4 sec and move on to 12:00:00 AM for the next day. I understand that without regular calibration, clocks go a little faster or slower after few months or years. I mean, whatever mechanisms are used to "conceal the loss" of few mins everyday, ppl can have an impression that one day on Earth is always exactly 24 hours (maybe no matter what). So the questions are, (1) Are there mechanisms for clocks, especially analog clocks, to tackle the issue of less-than-24-hours-a-day? and (2) Why do ppl keep communicating (for example, "the deadline is 11:59:59 PM local time") as if the "loss of 4 mins is not a great deal for errors so we just slow the clocks in the background just a little bit so nobody will notice the 4-min difference"?