I have a memory from school (admittedly many years ago), of staring at the big analog clock hanging up in the classroom, waiting for the class to end.
Occasionally, the minute hand would jump backwards by a minute - which was always very frustrating.
Am I remembering this correctly? Does anyone else have similar memories?
And if so - why did the clocks do that? And why only in classrooms? (Was it, as I assume, only because I was staring at the clock?)
I know that during the mid 1980s, my high school had what looked like an ordinary wall mounted, analog clock in every classroom. We were told that every one of these clocks were under central control from the main admin office and could be reset and adjusted by that central unit. I don’t know the truth of this but I do know that when daylight savings time rolled around, all the clocks consistently showed the same, correct time.
Perhaps your school had a similar system and the clocks were just being tweaked?
When I was a lad, the clocks were similarly controlled from a central location, because during the days that time changed, we would see the clocks go forward faster (in the spring) or turn backwards (in the fall) sometime in midday (presumably when the principal got around to do it - or after the secretary found the key that allowed the principal into the controls?).
I believe those clocks were all power line synchronized (to the 60 Hz AC mains) and occasionally needed an adjustment. Also remember being amused when they’d set them an hour ahead/behind for DST/standard time in the middle of class.
Google “Master Clock Systems”. They are common in schools. When I went to school in the 1960’s, they were all mechanical. There was a master clock in the front office which was used to control all the other clocks in the schools, like for resetting after power outages and daylight saving time.
These days, they’re more sophisticated, wireless, with web access, and possibly wifi and/or GPS.
My recollection is that all the clocks were synchronized by a master clock. While room clocks had hands, they were not analog. They would jump one minute every 60 seconds. The clocks were synchronized every hour in case they had drifted or missed one of the jump-one-minute signals from the office. At ten seconds before the hour, the minute hand would be released and it would point straight up, regardless of the position it was currently in. At five seconds before the hour, it would be set back to “59”. At the top of the hour (five seconds later), it would advance, as normal, to point to the “12”.
When I went to elementary school the teachers would check and reset the clock when the first bell rang in the morning. It was pretty easy, all they had to do was turn the hourglass over.
The memory that the OP triggered for me was the way those clock’s minute hands moved.
They didn’t move continuously all minute long. They sat absolutely motionless for 58 seconds.
On the 59th second, they would move backwards a bit, like a half-minute’s worth of distance.
Then on the 60th second, they’d snap forward to complete the minute.
Don’t know if that’s what the OP is referring to though. Probably not: I’d think the other kids would have been sufficiently observant to realize the hand wasn’t moving backwards in any kind of bad way, it was “cocking itself” in preparation for leaping forward to the next minute mark.
Holy cow, another buried memory resurrected on The Dope. At least I *think *it’s a memory. When I picture it, it’s almost as though actually I saw it in a movie. One of the John Hughes films, maybe?
Yes, this is exactly how I remember it, from the 1960’s. I hadn’t thought of that in years!
It was definitely in a movie, but which one??
Three O’Clock High?
Or was it a music video?
So. how did it work, back in the analog days? It’s all well and good to post “they were synchronized”, but HOW? What was the wiring diagram? Can anyone post an operator’s manual, installation manual, something? Because I think our tiny school had them, and we could barely afford rubber balls to throw at recess.
I have this vision of small diameter rods running through the walls, with gear boxes at every clock. And an adjustment wheel the size of a wheelbarrow tire in the office. 
Ohhhhh, I can picture that also. It’s going to drive me mental.
The simplest systems from ye olde days used pulses from the master clock to advance the remote clocks once per minute. I assume second hands were usually not synchronized. The system had to be started with all the remote clocks set to 12:00, then the master clock could sync them to the current time set on the master. It only requires a single wire to send a pulse signal to the clock to move ahead one minute. Some clocks had additional wires to advance one second or one hour at a time as well.
I don’t know how the clocks worked internally, but I assume a solenoid would advance a common clock gear mechanism.
That’s how it worked in my elementary school. Did it back off at 59 seconds or 58? I seem to recall it was more like a 2-second delay. Anyway, the clocks looked like the one on the left here signal - Control a synchronous slave clock - Electrical Engineering Stack Exchange and were actually recessed into the plaster walls. It wasn’t quiet system either. I remember once they had to set back the clocks to standard time during school hours but I guess the master controller only allowed the clocks to go forward. So imagine several minutes of clunk-thunk, clunk-thunk, clunk-thunk, as the clocks had to be rolled forward 11 hours all in one go. I wonder what the purpose of that leading back-off was. Maybe it helped keep the mechanism from seizing up over time by “wiggling” it every minute? That school was built mostly in the 1920s through the 1930s. Could the clocks be that old? I guess master clock systems did exist at the time.
The clocks in my high school looked like the one on the right in the photo above. I don’t recall them doing the clunk-thunk thing, or if they did, it was much quieter. Those would be from the 1950s and 1960s. The newer parts of my middle school which were built in the 1960s had the clocks integrated into a large metal backplate along with the intercom speaker. I seem to recall those being broken down more often. The clocks themselves were a good bit smaller, so maybe the mechanism wasn’t as robust.
Ferris Bueller? Fast Times in Ridgemont High? Something like that.
I remember it the same as AHunter3 (post # 8)
It’s in an episode of the Simpsons.