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Comment by jedberg | Hacker News Reader

The clocks in my elementary, middle, and high schools would do something similar. Not every minute, but every hour. At the top of the hour, when there was 15 seconds left, the second hand would make 3 second jumps until it hit the top, and then hold until the next hour started.

I always thought that was a brilliant way to keep mechanical clocks in sync. And the system had been there since the 1970s, so it was well before digital clocks were feasible for a school.

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The clocks in my schools would take 80 minutes to complete each hour. No wait. Maybe it only seemed like that.

Thanks for that. We had those as well. But third-grade me never really thought about the purpose. So it's fun to think about it now.

In contrast, I'll sometimes now walk into a lobby or reception area of a business where they will have like five different analog clocks on the wall representing NY, Paris, London, etc, (trying to look "international" I guess) and the minute hands are out of sync. Kind of sad in 2023. :-)

My gym has about 15 different clocks on the walls, and they all tell a different time, some of them egregiously so. Every few months (often after I mention it), someone will go around and fix the worst ones.

My first job was at a Network Operations Center, and it was just like in the movies, with a big projection monitor, two network operators at terminals below, and above us were four analog clocks depicting the four main time zones of these United States. They were electric, and I guess they were battery-powered because of the lack of cords going everywhere.

When Daylight Savings Time began, I sauntered in about 9am and my coworkers were filtering in too. The morning guy, "Matt" had been there since about 6am and he had changed the clocks. So my other coworker, "Jason" congratulated Matt for setting all the clocks correctly and then he asked him, "so did you do it by setting all four clocks ahead one hour, or did you move them all to the left and then move the Pacific clock to the Eastern position?" Facepalm!

That might be a good job interview question, or it would have been if manual, analog clocks were still a thing.

That's one good thing about daylight savings time, I suppose: It's a good opportunity to correct any non-synchronized clocks.

Or to haphazardly ruin any synced ones.

I raise my glass, half empty, to you! you and me, we're the optimists, things can only get better from here!

Reminds me of the old saying, "A person who has a watch always knows what time it is. A person who has two watches is never quite sure."

And this is why I don’t like digital Vernier callipers. :P

It'd be a fun project to make a dial wall clock that uses GPS time.

GPS would be tricky to receive in a typical hotel or office lobby (i.e. far away from any windows at the ground floor, possibly in an urban canyon).

In Germany (and in neighboring countries), radio-controlled clocks are quite common for this purpose, listening to DCF77 near Frankfurt [1].

Long wave seems to work a bit better than the L-band for indoor propagation, and it probably also helps that the transmit power is three orders of magnitude higher.

I'm not sure if the US has an analogous service – there's WWV and WWVH, but they are shortwave transmitters, and I don't know if wall clock or even wristwatch size receivers are possible for that.

[1] https://en.wikipedia.org/wiki/DCF77

> I'm not sure if the US has an analogous service – there's WWV and WWVH, but they are shortwave transmitters, and I don't know if wall clock or even wristwatch size receivers are possible for that.

It does. Small WWVB clocks that self set are quite common.

Yes, works for small clocks and watches, but they have mostly moved to gps these days, at least for auto sync watches.

WWVB is running at 60kHz, and powers at least a few of the small desk clocks in my home :)

https://en.m.wikipedia.org/wiki/WWVB

I think you can still buy NTP reference devices for your network that use GPS. So, the lobby of the hotel doesn't have to be within view of the sky, as long as their reference device is.

Meinberg is just one of several companies I've seen that sell clocks that are NTP clients.

It makes sense that a company might make those, if they also make the NTP servers that those clients might be connected to.

Good stuff. I'm planning on buying some for the house.

Our elementary school clocks (70s) made a variety of nearly imperceptile sounds as they got near the top of the hour, or turned it over. We were like dogs when they hear the about-to-eat sounds start.

Pavlov was sitting in a bar when the last order bell rang. "Oh shoot! I need to feed the dogs" he thought.

How did they know when the next hour started without digital communication?

The details depended on the system. The most common arrangements were either polarity (hour pulse opposite polarity of minute pulse) or a separate wire for hour pulse. Later systems introduced serial digital communications but were never as widely installed as the minute and hour pulse systems in schools.

They had digital communication just not cheap ICs. I don't know how it worked but I imagine it was something like a mechanical switch that held the minute hand until it got a signal from the main office to start moving again.

The clocks could even be set for Daylight time centrally, so I assume it had a way to send a signal that triggered a motor to move the hour hand faster.

Since it's a school I wonder if they could just hold them back 1 or 11 hours on the weekend for DST changes. This would eliminate the need for an additional signal and circuitry on each follower clock.

In the Standard Electric Time Company slave clocks that I've got, the master sends about a 12ms pulse once a minute, which pulls in a solenoid and allows a lever to ratchet one tooth on the minute wheel and advance the movement. Then once every twelve hours, the master sends a longer pulse, which pulls in a stronger second solenoid that allows the wheel to turn freely. There's a weight on the hour wheel which will pull the wheel around until the weight is on the bottom because of gravity, which corresponds with 12 o'clock. So no matter where the clock is, it will fall back to twelve with the longer pulse, and then begin the ratcheting again with the once a minute shorter pulses.

(Sorry for the deprecated master/slave terminology, it's unfortunately what they used at the time)

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