Where does my computer get the time from?

The draft of the version upgrade explains the possible uses of this: https://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.8213-draft...

Mostly, it's so the public can verify events that were supposed to be random really were random. The executive summary gives plenty of examples, but think of a pro sports draft lottery. Fans always think those are rigged. They could simply use these outputs and a hashing function that maps a 512-bit block to some set with cardinality equal to the number of slots and pre-assign slots to participating teams based on their draft weight. Then fans could verify using this public API that the draw the league claims came up randomly really did come up randomly.

People always think polls are rigged. This could be used to publicly produce random population samples for polling.

This was also used to prove a Bell inequality experiment worked with no loopholes.

See https://news.ycombinator.com/item?id=37783764

>It's not a blockchain, but a single writer Merkle DAG.

Hmm. Just because something's a Merkle DAG doesn't make it useable on the Internet. A single-writer blockchain, perhaps?

Oh… so you are calling a database a “block chain”.

People keep saying Merkle DAGs when someone calls a linear chain of recursively hashed data blocks a blockchain.

I don’t understand.

My understanding of the Merkle Tree is that it’s a recursive hash, but the leaf nodes are the data, each layer up the tree is the hash of the child nodes.

In a merkle tree, only the leaf nodes store (or reference) data, everything else is just a hash.

Is there another merkle structure I don’t know about?

https://en.wikipedia.org/wiki/Merkle_tree

If the nodes with hashes contain data, it’s not a merkle tree.

If each block contains the hash of the previous block, then I think that it is a blockchain (regardless of if there is multiple authors or only a single author). A git repository is a blockchain, too.

Ok but then anyone in control can change the entire tree, why need this Merkle tree?

> No consensus necessary. Much like a git repository with a single author.

But shouldn't we want decentralized consensus for this?

What if NIST's key(s) were to get compromised, or the org were to disband or become corrupt/dysfunctional?

It kinda makes you wonder why desktop computers don't use the AC frequency as a stable-ish time source. Short-term accuracy is pretty poor, but it can definitely do better than 12 seconds over a week!

There’s a fun thing about quartz wristwatches: one of the biggest contributions to frequency fluctuations in a quartz oscillator is temperature. But if it is strapped to your wrist, it is coupled to your body’s temperature homeostasis. So a quartz watch can easily be more accurate than a quartz clock!

Really good watches allow you to adjust their rate, so if it runs slightly fast or slow at your wrist temperature, you can correct it.

One of the key insights of John Harrison, who won the Longitude prize, was that it doesn’t matter so much if a clock runs slightly fast or slightly slow, so long as it ticks at a very steady rate. Then you can characterise its frequency offset, and use that as a correction factor to get the correct GMT after weeks at sea.

> After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 = 12 seconds.

Where are you getting that 12 from?

That's a neat way of ensuring that time never jumps backwards on your system!

Reminds me of the same idea but applied in the opposite way in some train station clocks: Their second hands take slightly less than a minute to complete one rotation, after which they stop and wait for a signal sent from a central clock to be released simultaneously.

Making a clock run slightly slow or fast is much easier than making it run just about correctly :)

I worked on an embedded video system once where no one took into account the slight difference between the encoder and decoder clock frequencies. If the encoder was slower, no problem, you dropped a frame every once in a while. If the encoder was faster, you would buffer frames up to the memory limit of the system. Since these systems were typically left on for weeks at a time, the pilots would eventually discover the video they were using to fly a vehicle was several seconds in the past. Luckily this was discovered before initial shipment and the code was changed to drop everything in the buffer except the latest video frame.

The linked PDF has clear page delineations, unlike the HTML page: https://ripe86.ripe.net/presentations/134-2023-04-whence-tim...

I mean, put a little gnome hat on him and I’d believe it…

When I gave the talk, I showed the slide before I talked about it. It’s normal to show the speaker notes below the slides in software like Keynote or Powerpoint.

It's simply not intuitive in the way it was presented that the line of text was a footer for the picture. The text and pictures are mistakenly read as belonging to the same "layer", sequentially, which is not what the author intended. It's obvious what that intent was, but it's not structured correctly to be properly interpreted.

I was really bothered that on the website version, the NTP packet diagram is largely illegible. I hope that when they gave this talk on slides, you could read it.

Or when Netgear flooded the University of Wisconsin by hardcoding their NTP server's IP address into some of their home routers:

https://pages.cs.wisc.edu/~plonka/netgear-sntp/

Do you have a link for what you are doing now? Seems interesting!

When time was based on earth rotation, astronomers used “transit instruments” to observe when certain “clock stars” passed directly overhead. The clock stars had accurately known positions, so if you routinely record the time they pass overhead according to your observatory’s clock, then you can work out how accurate your clock is.

Newcomb’s data would have been accurately timed observations, as many as he could get hold of, going back about two and a half centuries.

Please tell me you just coined this.

That’s hilarious.

Stratum 0 is the reference clock itself; stratum 1 is an NTP server attached to one or more reference clocks. https://www.ntp.org/ntpfaq/ntp-s-algo/#5111-what-is-a-refere...

Time based OTP is pretty sensitive though. Probably that is what broke?

They might have been using kerberos authentication?

Kerberos is very particular about time.

You are correct and I believe it was Kerberos that we were locked out of on this system since it was running a SMB share.

Laurens Hammond invented the synchronous electric motor once A/C domestic voltage had proliferated enough as an alternative to the original D/C electrification first established by Edison.

This made it possible for the first time to build clocks based on the stable frequency of the incoming A/C supply voltage, much more reliably than those based on the incoming line voltage, which varies quite a bit whether it is A/C or D/C.

This put him on the map as a manufacturer when he went forward to build Hammond clocks commercially.

Years later his engineers encouraged him to consider developing an electric church organ, which would be possible to remain in tune regardless of variations in line voltage themselves.

Hammond was not musically inclined but he did it anyway.

Right up there with the Great Men in the most legendary way.

http://thehammondorganstory.com/

By the time the 1960's came around, almost all new American vehicles were recognized as modern Space Age conveniences, and a factory clock (mechanical analog, naturally) had become almost a universal standard accessory beyond the most budget price points.

There were a couple drawbacks to the factory clocks, they had to be connected to the car battery at all times to keep running, they didn't drain the battery very much at all but still would eventually deaden it if undriven, way worse than no clock. And they depended on the incoming voltage which determined the internal clock motor speed to begin with. Different automotive electrical systems and batteries themselves do vary perhaps 10 percent about a nominal design voltage of 12 VDC. There is no stable A/C in the car that a synchronous motor would need to run on[0].

These now-vintage clocks were self-correcting. You correct them yourself. Actually the same twisting of the knob to move the hands of the clock, which was familiar from earlier non-correcting clocks simply did the job. So they were somewhat backward-compatible. Only the Space Age units had smart enough mechanical ability to take into account how much and in which direction you moved the hands, and adjusted the previous running speed accordingly. If the clock was not very close to correct time when you adjusted it, it would take repeated adjustments over a number of days or weeks to get it to very realistic speed. All it really did was successive approximation. You had to supply your own natural intelligence.

Even at the time lots of drivers never knew this, and there was widespread disappointment over the wildly inaccurate clocks "which were OK when new but went downhill 'through time'". They only added maybe a dollar to your car payment but that was very expensive compared to a highly reliable cheap household clock at the time.

When you think about it, today lots of drivers are not quite up to par when it comes to engaging the amount of natural intelligence that would be needed in many other ways besides timekeeping.

[0] The electrical "vibrator" which provided switch-mode 12VAC which could be stepped up by a transformer to supply much higher voltage to power vacuum tube radios still produced a variable A/C voltage & frequency, dependent on the underlying D/C supply voltage.

Correct. Oscillators are subject to drift through a number of means, and they all have ridiculous effects too. https://news.ycombinator.com/item?id=37613523

Oh, it gets better. I used to get reminders in the mail to take my luxury car into the dealership for "service" to adjust the clock twice a year. Or I could ... you know, just press a few buttons for free.

The trouble with all the modern cars that have synchronized clocks is that, well, you've already put in an LTE SIM card, so why not send up some telemetry at the same time? And here we are, with cars that are surveillance devices with four wheels.

DST policies vary by country and (US) state. The US DST schedule can be changed, and has been — twice in the last 50 years. There are proposals to do so again, both nationally and within states. Implementing automatic DST adjustment puts you on the hook for software updates forever. It’s much easier to just let people change the time manually when they need to, like they do with other appliances.

IMHO, the real failure is when devices make it hard to figure out how to change the time.

Oooooh decades later I finally get the name Slashdot! Thank you!

I would have enjoyed it tremendously.

I think the poster is getting at the fact they had a CDMA phone - those require extremely tight clock synchronization in order to work. Like a phone needs a sub-chip level of synchronization to a base station (order of a few hundred ns) otherwise it won't be locked to the relevant codes.

All this is down at the modem layer and was probably not externalized to the crappy CPU that ran the OS for the phone though.

You can still use the CDMA networks to get a very precise time reference, suitable for a stratum-1 timeserver, but I think not for very much longer.

It isn’t just the difference in rate. The main content of Circular T https://www.bipm.org/en/time-ftp/circular-t is the time offset of the various national realisations of UTC. Another important aspect is characterizing the stability of each clock, which determines the weighting of its contribution to UTC.

The algorithm behind Circular T is called ALGOS.

And not just one, millions of them.

I get the confusion for the US Navy though, as the clock is at the US Naval Observatory.

If you ever need the time, just call (719) 567-6742

"US Naval Observatory, Master Clock, at the tone, Mountain daylight time, nine hours, sixteen minutes, fifteen seconds...beep!"

The USA has two main time labs: the USNO, which provides time and navigation for the DoD, including the GPS; and NIST which provides time for civilian purposes, including WWV. NIST tends to do more research into new kinds of atomic clock (eg optical clocks, chip-scale clocks) whereas the USNO does more work on earth orientation.

The USNO atomic clock ensemble includes caesium beam clocks, hydrogen masers, and rubidium fountains. NIST uses mostly hydrogen masers, and fewer caesium beam clocks, though their primary frequency standards are caesium fountains.

You are sort of correct. NTP is pretty decentralized. DNS has a few specific servers (root servers) that all DNS eventually hits to find where to get a result, but, the 'tree' of DNS resolution is much different from that of NTP, which doesnt have such a tree, except as defined by any DNS entries, if they are used (ex pool.ntp.org has many A records for many ips or CNAMEs to other domains (ex 0.pool.ntp.org)).

There are many contributors to the official timekeeping. Most facilities who do science will have their own actual atomic clock, which they then share out the data, in the form of an NTP server, however, they will not typically use data from the rest of the world, except for correlation events. The rest of the world relies on a handful of clocks which are either from NIST (ntp.org I think is owned by them), or from major providers like cloudflare (not sure they have an ntp server available the public can use, im almost certain that they would use their own atomic clock internally for security reasons), microsoft also has one, i think, afaik they would need to because they provide their own ntp pool, but they may just aggregate from multiple NIST servers.

You can setup your own NTP server as well, and setup systems you own to start using it instead of whatever is configured. And, if one were so inclined, could even find and run your own atomic clock, and register it with the ntp pool. Im actually not sure the atomic clock is required, id hope it would be, but idk.

I think chronyd is the one you want running on your Linux computer. IIRC it uses NTP to adjust your system clock over time for more accuracy besides just setting the time with NTP. And has more options for more time-nutty things.

GPS seems like a better choice for a cell tower.

It gives me an idea of training my dog to hit a button to get food and eventually plot the data onto a graph. Would be funny to draw some patterns from it

That’s so interesting. My dog runs on a solar clock. He starts begging for his dentastick when it gets dark out, and stays in bed until the sun comes up in winter.

We started using an automated feeder with our dog. It broke one day and we were surprised to see that he was prompting us to feed him almost exactly at the programmed times. Like down to the minute.

Not sure if he’s relying on other sensory information like certain smells or sounds. I don’t believe that’s the case; we didn’t replace the broken feeder for 3-4 months and he was able to keep time within a few minutes during that period. Our behavior is erratic and changes often; we work jobs with very inconsistent schedules (thus the automatic feeder) so it’s likely not that our behavior is prompting him as well. We can even observe him consistently going to his feeding area on the security camera at the correct time when no one is home. Interesting stuff!

Think about the number of pets doing this at, say, 20:07, and owners not realizing the time accuracy because it's not a round number of minutes after the hour.

maybe add an NTP reference clock to biff¹

...or add it to systemd (it will get there eventually anyway)

[1] https://en.wikipedia.org/wiki/Biff_(Unix)#Origin_and_name

I suspect in cases like this the dog is hearing something you don't in the environment and has associated it with treat time, creating the expectation. If you reconfigure NTP to use her intuition, you risk biasing whatever the source is, creating a feedback loop that will create drift.

Only one? It's recommended to keep at least two as they are very social animals.

My four live in the garden, well protected and I'm too chaotic to keep any sort of regular feeding schedule, but they are fine with that, must be exciting for them if an unexpected feed of carrots or cucumbers drops.

My dog is the same. I have a friend who spends the day at my house every Thursday. The dog sits by the door waiting, but only on Thursdays!

Exactly the same here with my golden doodle. We feed her dinner at 4pm and she’s pretty much always off-by-one and comes to check on the status at 3.

Girlfirend's minpin-chihuahua mix is like this. Thinks its breakfast time well before it is, indeed, time for breakfast.

There was this BBC documentary where they tracked cats with GPS called The secret life of cats where they found this behavior. The cats would also visit each others house at different time and eat from each others food.

cat law sounds hard. cat lawyers must make a fortune litigating in cat court

Reminds me of the feynman book "What do you care what other people think?"

There's a chapter:

“It’s as Simple as One, Two, Three…”

where he talks about and experiments with mental counting and mental time judgement

I decided to investigate. I started by counting seconds—without looking at a clock, of course—up to 60 in a slow, steady rhythm: 1, 2, 3, 4, 5…. When I got to 60, only 48 seconds had gone by, but that didn’t bother me: the problem was not to count for exactly one minute, but to count at a standard rate. The next time I counted to 60, 49 seconds had passed. The next time, 48. Then 47, 48, 49, 48, 48…. So I found I could count at a pretty standard rate.

Now, if I just sat there, without counting, and waited until I thought a minute had gone by, it was very irregular—complete variations. So I found it’s very poor to estimate a minute by sheer guessing. But by counting, I could get very accurate.

he goes on to do all kinds of other experiments like counting while running up and down stairs and more... :)