Time.is

Post by dfc » Sun, Mar 11, 2012, 7:54 PM UTC

phillmv wrote: post #58

roryokane wrote: post #50

I'm wondering how atomic clocks in general get set in the first place. Did, at some point, scientists calculate when the sun was exactly overhead Greenwich and call that noon? Because I would think that that calculation would have a multi-second error, so setting your clock to the second would be pointless. Or maybe there is no such thing as "actual physical time" and there is only what people have agreed to call the…

Well… it's an arbitrary standard. We just call a day one full rotation of the earth, and we just happen to divide it into 24hr periods with 60 subdivisions. Theoretically, you could measure the rotation of the earth and call that a day, but I have no idea how you would measure that down to the millisecond. As to "Real Time", I don't know about the specific legalities, but the standard goes as follows: everyone uses U…

Post by dfc » Sun, Mar 11, 2012, 8:00 PM UTC

apaprocki wrote: post #56

mwexler wrote: post #14

I like Time.gov, personally; it was the first site I ever found around this concept and so it has a soft spot. I keep finding all my physical atomic clock synced clocks (yes, I have more than one, they are cheap these days) disagreeing, sometimes by 2 seconds or more, which makes me laugh (great ideas ruined by poor implementation). I find many of the web sites (listed in comments or the original post) to also differ…

In order to achieve the highest possible accuracy, you have to bring in your own hardware. We use appliances with internal rubidium oscillator clocks which also synchronize with the signal from all visible GPS satellites. This is as good as one can get if you really want to ensure proper time without having an external dependence on a third party or network. edit: A paper from 1989 on the subject: http://tycho.usno.n…

Post by dfc » Sun, Mar 11, 2012, 8:03 PM UTC

gwern wrote: post #36

Your clock is 0.2 seconds slow. Accuracy of synchronization was ±0.625 seconds If the result is within the margin of error, wouldn't it be better to just not tell me at all?

Post by tlb » Sun, Mar 11, 2012, 8:11 PM UTC

dfc wrote: post #63

apaprocki wrote: post #56

Earlier quoted context omitted.

In order to achieve the highest possible accuracy, you have to bring in your own hardware. We use appliances with internal rubidium oscillator clocks which also synchronize with the signal from all visible GPS satellites. This is as good as one can get if you really want to ensure proper time without having an external dependence on a third party or network. edit: A paper from 1989 on the subject: http://tycho.usno.n…

But you are relying on a third party / network. Your rubidium clock is only good for accurately measuring the length of a second. It has no idea when a UTC second begins. You are relying on GPS time in order to know when the UTC begins. You need time and frequency for "proper time."

Post by dfc » Sun, Mar 11, 2012, 8:20 PM UTC

tlb wrote: post #67

dfc wrote: post #63

Earlier quoted context omitted.

But you are relying on a third party / network. Your rubidium clock is only good for accurately measuring the length of a second. It has no idea when a UTC second begins. You are relying on GPS time in order to know when the UTC begins. You need time and frequency for "proper time."

You can measure the angle of the sun to sync with UTC. I believe you can get within seconds using commodity equipment.