# 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:** 20\ **Page:** 4
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 30, 2025, 8:12pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/61 "2025-04-30T20:12:45Z")
Sorta the electromechanical equivalent of [![](https://imgs.xkcd.com/comics/nerd_sniping.png) ](https://imgs.xkcd.com/comics/nerd_sniping.png) ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [May 1, 2025, 2:42am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/62 "2025-05-01T02:42:28Z")
> [@XOldiesJock](#): > > Having worked for CBS Radio several years ago (when CBS still owned radio stations) it was standard procedure for all of their stations to be on a 15 second digital delay at all times, even the music stations, just in case someone said something they shouldn’t have. What you’re hearing on your radio is the delay. I would think the current owners (Audacy) would have the same procedure in place. If that’s the case, and the on-air hosts know that they’re on a 15-second delay, the chime should ring 15 seconds early. With the delay, they’ll ring at the correct time. I had something similar happen a couple years ago. I was at the Kennedy Space Center watching a rocket launch. They had TVs set up showing the NASA coverage of the launch. One of the docents told us that the TV was delayed by 9 seconds. We started our 10-second countdown when the TV was at 19. I’ve always kinda wondered how the delay on live broadcasts worked in practice. There must be someone listening to the hosts for any objectionable words, who can then quickly switch to the delayed signal to bleep out the offending word. That seems to create a loophole. If someone swears twice, 15 seconds apart, the monitor will miss the second one because he was busy bleeping the first one. ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [May 1, 2025, 10:40am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/63 "2025-05-01T10:40:26Z")
> [@Pardel-Lux](#): > > A story that made the rounds ages ago was that a vengeful ex-girl friend called the time phone number in Tokyo and did not hang up before leaving the room and closing the door. Here they tell the story of a vengeful ex-girlfriend who called the time phone number in New York. The story was of an office romance with a married boss and his secretary. He dumped her just before he left with his family to go back to the States for a couple of weeks. She made the call from his office. I first heard this in the 80s, when international calls were insanely expensive. It was told as an obvious joke so I think that urban legend has been going around for a long time. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [May 1, 2025, 12:40pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/64 "2025-05-01T12:40:47Z")
Yes, the '80s would be about right. Funny how these stories made the rounds before internet virality. You heard it in Tokyo? I heard it in Berlin. And international calls were indeed insanely expensive back then. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 1, 2025, 2:21pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/65 "2025-05-01T14:21:20Z")
> [@Bullitt](#): > > Does anyone else here like to know the current, precise time down to the second? How do you determine that? I do! I wish my iPhone and iMac displayed seconds on all time displays including photos. Actually, I wish fractional seconds were displayed on photos, because they can be taken much less than a second apart. Time is a great way to identify and sort theem. I used to do scientific research on big machines. Sometimes I’d have multiple data loggers on them, because I had so many channels or because the machines were so long that running small analog signals through long enough wires would introduce noise. In these cases, subsecond timing was important when comparing measurements (such as how fast a pressure change propagated along the length of the machine). For these situations I wrote a program that could get subsecond accuracy setting the data loggers (DataTaker DT800) through their RS232 port. Then I’d also log digital transitions to use as internal comparison timestamps through postprocessing. I like GPS time. I’ve toyed with buying a Stratum 2 receiver for my home network, but until I do, I’m using NTP. On my iPhone I have a couple of apps that read NTP servers; one emits clicking sounds and displays 100 points in a circle to mark tens of milliseconds, and the other reads multiple servers and displays an intercomparison. I have two six-digit NTP wall clocks. I set my camera clocks from them, and sometimes go as far as taking photos of the seconds transitions to estimate photo timestamp accuracy. I’ve also photographed the wall clocks with the iPhone app to compare. > [@Whack-a-Mole](#): > > In the US, NIST is the official time. As accurate as you can get. Agreed. But there’s a certain subtle qualifier needed. NIST makes available a current time through radio transmissions, but that’s a tentative time. The final determination of accurate time is done retroactively by comparison of multiple sources later. IIRC it’s something like a month later, though I could have this delay wrong. You can record the time of an event to the highest resolution you can, and weeks later you can adjust it to improve its accuracy. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [May 1, 2025, 2:53pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/66 "2025-05-01T14:53:27Z")
This is profoundly messed up. As I mentioned above, I could walk to the broadcast facility for WWV. I offered that I could simply head over there and ask them what the time is. But you’re saying I have to ask them what the time _was?_ And if I do that, how will I reference _when_ I’m talking about? This sounds needlessly epistemological, metrological, circular, confusing, and anxiety-provoking. I’m getting a sundial. QED ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [May 1, 2025, 3:03pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/67 "2025-05-01T15:03:27Z")
You will to have gotten a sundial ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 1, 2025, 3:04pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/68 "2025-05-01T15:04:33Z")
Paid for next Tuesday I hope. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 1, 2025, 6:09pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/69 "2025-05-01T18:09:28Z")
Be sure to get one that compensates for atmospheric refraction. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [May 1, 2025, 7:30pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/70 "2025-05-01T19:30:23Z")
I’m sorry. I may have mist something, because I haven’t the foggiest notion what that meant. 😉 ---
**Author:** ![Dorjan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dorjan/32/12440_2.png) [@Dorjan](https://boards.straightdope.com/u/Dorjan)\ **Post date:** [May 1, 2025, 7:39pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/71 "2025-05-01T19:39:18Z")
Interestingly, my phone (Android) time display is a few fractions of a second faster than the time on the NIST website. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 1, 2025, 7:47pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/72 "2025-05-01T19:47:59Z")
[Atmospheric refraction](https://en.wikipedia.org/wiki/Atmospheric_refraction) causes the sun to appear to be slightly higher than its true position (the position at which it would be observed if there were no atmosphere). The effect is largest when the sun is low in the sky. A naively constructed sundial will therefore be slightly wrong in the early morning and late evening. Since the discussion in this thread is about precision time measurement, I was making a small joke about one effect that contributes to the inaccuracy of sundials. ---
**Author:** ![DavidNRockies](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidnrockies/32/6279_2.png) [@DavidNRockies](https://boards.straightdope.com/u/DavidNRockies)\ **Post date:** [May 1, 2025, 7:49pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/73 "2025-05-01T19:49:00Z")
> [@markn\_1](#): > > I was making a small joke about one effect that contributes to the inaccuracy of sundials. And _I_ was making an even smaller joke about two possible factors that can cause atmospheric refraction 😉 ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 1, 2025, 8:25pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/74 "2025-05-01T20:25:27Z")
Perhaps you two should sit down and reflect a bit on what you’ve done before throwing shade on one another’s gnomon. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 2, 2025, 3:26am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/75 "2025-05-02T03:26:58Z")
> [@LSLGuy](#): > > …gnomon… TIL. I look forward to the day I win Trivial Pursuit with that tidbit. ---
**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:** [May 2, 2025, 11:23am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/76 "2025-05-02T11:23:51Z")
> [@DavidNRockies](#): > > I’m getting a sundial. QED I bought one from a local guy who created a unique design for one! It is customized for my house location, so if I ever move out the sundial stays with the house. **Daniel Wenger’s sundial** ➜ [The Wenger Sundial](http://wengersundial.com/indexformer.htm) ■ Daniel lives about an hour away, in Santa Cruz. I found him through NASS, the North American Sundial Society. It does not, however, provide the precise seconds. I’ll have to file a complaint, LOL. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [May 2, 2025, 4:09pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/77 "2025-05-02T16:09:42Z")
> [@Whack-a-Mole](#): > > > [@LSLGuy](#): > > > > …gnomon… > > TIL. I look forward to the day I win Trivial Pursuit with that tidbit. I always thought it was part of some archipelago, somewhere ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [May 2, 2025, 5:12pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/78 "2025-05-02T17:12:12Z")
> [@LSLGuy](#): > > Perhaps you two should sit down and reflect a bit on what you’ve done before throwing shade on one another’s gnomon. I’m looking into how to acquire a second home on DiscWorld. Not sure about the visa requirements etc? The sun there is a _proper_ sun that behaves in accordance with Narrativium…? ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 3, 2025, 2:30pm UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/79 "2025-05-03T14:30:35Z")
> [@DavidNRockies](#): > > This is profoundly messed up. > > As I mentioned above, I could walk to the broadcast facility for WWV. I offered that I could simply head over there and ask them what the time is. You could ask them what UTC(NIST) is. The actual UTC is calculated later. That is to say, a record of the differences between UTC(NIST) and UTC is calculated and published later. If you recorded UTC(NIST), you can correct it to UTC. This might be important for, say, stellar occultation data. " The concept of a virtual time scale can be difficult to grasp, but perhaps becomes easier when you consider that none of the clocks in the UTC ensemble reside at the BIPM and thus the BIPM doesn’t measure any physical clock signals. Instead, the BIPM calculates UTC from measurement data that is sent to them by the more than 80 laboratories mentioned earlier. […] Once a month, after all clock measurements have been collected and after all calculations are complete, the BIPM publishes the results in an on-line document known as _Circular T_. This document lists the time difference between UTC and each of the local time scales that are subsets of UTC, such as UTC(NIST). In _Circular T_ parlance, the local time scales are known as UTC(_k_), where k is a variable that designates the name of the local time scale’s laboratory, and where values for UTC – UTC(_k_), are reported at 5-day intervals. The publication of these values is extremely important for ensuring that UTC is indeed “coordinated” around the world, because it verifies the accuracy of each UTC(_k_) time scale with respect to UTC. […] To make data available more frequently than once per month, the BIPM also publishes an unofficial time scale called Rapid UTC, or UTCr. Rapid UTC is published once per week, with values of UTCr – UTC(_k_) reported at 1-day intervals. Currently (November 2020), NIST and more than 60 other laboratories participate in UTCr. Although the values computed by UTC and UTCr are not known until after the fact, UTC(NIST) is continuously adjusted using forward prediction techniques that anticipate where UTC will be when the _Circular T_ is published. As a result, UTC(NIST) is an excellent approximation of UTC that has the advantage of producing physical signals in real time, and that typically differs from UTC by less than three billionths of a second (3 ns). […] [[https://www.nist.gov/pml/time-and-frequency-division/time-realization/utcnist-time-scale-0/introduction-utcnist](https://www.nist.gov/pml/time-and-frequency-division/time-realization/utcnist-time-scale-0/introduction-utcnist)] 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. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [May 10, 2025, 12:15am UTC](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657/80 "2025-05-10T00:15:08Z")
> [@Robot\_Arm](#): > > > [@Whack-a-Mole](#): > > > > > [@LSLGuy](#): > > > > > > …gnomon… > > > > TIL. I look forward to the day I win Trivial Pursuit with that tidbit. > > I always thought it was part of some archipelago, somewhere No one is going to take the bait on that one? [Previous page](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657.md?page=3) [Next page](https://boards.straightdope.com/t/what-time-is-it-how-do-you-determine-the-current-precise-time/1017657.md?page=5)