# What time is it? How do you determine the current, precise time? **URL:** \ **Category:** Factual Questions\ **Created:** [April 29, 2025, 2:35pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657 "2025-04-29T14:35:34Z")\ **Posts on this page:** 8\ **Page:** 5
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 10, 2025, 12:16am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/81 "2025-05-10T00:16:33Z")
Gno, mon. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [May 10, 2025, 12:38am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/82 "2025-05-10T00:38:54Z")
> [@Napier](#): > > By the way, if you walk over there to ask them, and you care about getting the most exact version, stand close to whomever you ask. At a typical conversational distance of three feet, the time for light to travel from them to you is about equal to the discrepancy between UTC(NIST) and UTC. Yeah but the sound delay will be in milliseconds. I don’t think you’d be able to stand close enough to compensate better than 3 nanoseconds. 🗣 💨 👂 ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [July 15, 2025, 11:39pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/83 "2025-07-15T23:39:47Z")
About [Time.gov](http://Time.gov) – At noon, it shows 12:00:00 for one second. Obviously, the time is exactly noon for only an instant. So when is it exactly noon? The start of the second, or the end, or the halfway point? If you’re the one setting it up, you likely would decide the best way to do it is put exact noon at the halfway point – in other words, when the clock shows 12:00:00 then that’s the correct time, rounded to the nearest second. In any case, I believe that’s what they did. How do we know what they chose? By comparing it with WWV or 303-499-7111, where 12:00:00 UTC is at the start of the tone that sounds every sixty seconds. By the way: the phrase “current, precise time” is some ambiguous. You’ve heard of leap seconds? Once in a while, official time 12:00:00 comes exactly 61 seconds after official 11:59:00. So – should you call those times “precise”, when the minute is 61 seconds long? Official time is based on atomic clocks. As you’d expect, Earth doesn’t keep as accurate time as an atomic clock, so Earth Time slowly diverges from atomic-clock time, where each day is exactly 86400 seconds, each second being so many vibrations of a Cesium atom. What to do? Use what’s called UTC instead of straight atomic-clock time. A UTC day is always 86400 seconds, except when they’ve decided it’s time to add a leap second, because Earth Time has fallen behind UTC a half-second or so. WWV and 303-499-7111 both try to tell you the current difference between UTC and Earth Time, in tenths of a second. I suppose they can’t be more precise than that, since determining Earth Time does take time. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 15, 2025, 11:52pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/84 "2025-07-15T23:52:34Z")
> [@Timz](#): > > So when is it exactly noon? The start of the second, or the end, or the halfway point? None of the above? If you need to know “exactly” when some transit is going to be taking place, forecast values for UT1 − UTC are published by the International Earth Rotation Service. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [July 16, 2025, 12:18pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/85 "2025-07-16T12:18:12Z")
> [@Timz](#): > > So when is it exactly noon? The start of the second, or the end, or the halfway point? From what I’ve seen, times are truncated, so “the start of the second” – that is, to the extent that the method of rounding is the controlling issue. ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [July 16, 2025, 6:19pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/86 "2025-07-16T18:19:03Z")
At 303-499-7111, the start of the tone each minute is supposed to the actual UTC time. If you listen to it while you watch the time change at [Time.gov](http://Time.gov), you’ll see it’s actually 12:00:00 about a half-second after the [Time.gov](http://Time.gov) display changes to 12:00:00. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [July 16, 2025, 8:04pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/87 "2025-07-16T20:04:46Z")
> [@Timz](#): > > 303-499-7111 Cool. Thanks for that. And welcome to the dope @Timz ! ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [July 16, 2025, 8:23pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/88 "2025-07-16T20:23:29Z")
Now that I’m retired, I don’t really care what the exact time is, if I ever did. I don’t wear a watch any longer, but have my old Timex Indiglow next to the bed so I can see if I’m close to getting up or not. I haven’t set an alarm in years. I have a digital clock under the TV so I can see if the news is coming up or if it’s getting close to leaving time for some event. It’s a minute off; I’ve gotten used to it. [Previous page](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657.md?page=4)