5 ms·

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

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.

smm11 4y ago
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.
- woleium 4y ago
  Pavlov was sitting in a bar when the last order bell rang. "Oh shoot! I need to feed the dogs" he thought.
bmitc 4y ago
How did they know when the next hour started without digital communication?
- jcrawfordor 4y ago
  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.
- jedberg 4y ago
  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.
  - tdeck 4y ago
    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.
- technothrasher 4y ago
  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)
  - Slava_Propanei 4y ago
    [dead]
jimmydddd 4y ago
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. :-)
- ipqk 4y ago
  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.
  - Eleison23 4y ago
    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.
  - lxgr 4y ago
    That's one good thing about daylight savings time, I suppose: It's a good opportunity to correct any non-synchronized clocks.
    - stavros 4y ago
      Or to haphazardly ruin any synced ones.
spindle 4y ago
The clocks in my schools would take 80 minutes to complete each hour. No wait. Maybe it only seemed like that.
deleted 4y ago
[deleted]

smm11 4y ago

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.

woleium 4y ago
Pavlov was sitting in a bar when the last order bell rang. "Oh shoot! I need to feed the dogs" he thought.

bmitc 4y ago

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

jcrawfordor 4y ago
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.
jedberg 4y ago
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.
- tdeck 4y ago
  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.
technothrasher 4y ago
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)
- Slava_Propanei 4y ago
  [dead]

jimmydddd 4y ago

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. :-)

ipqk 4y ago
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.
- Eleison23 4y ago
  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.
- lxgr 4y ago
  That's one good thing about daylight savings time, I suppose: It's a good opportunity to correct any non-synchronized clocks.
  - stavros 4y ago
    Or to haphazardly ruin any synced ones.

spindle 4y ago

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

deleted 4y ago

[deleted]