Clock

[azurelunatic]

I seem to recall a logic puzzle presented to me when I was but a chick: so a householder has a fine grandfather clock, which keeps excellent time; s/he/* sets it every year on the summer Solstice when the sun is highest in the sky. There are other, lesser, clocks in the house, not in sight of the grandfather clock. How may these clocks be kept in time?

The answer, as it was originally presented to me, was that the householder obtains a watch, synchronizes the watch with the grandfather clock, and then uses the watch to set the rest of the household clocks.

That answer always left me vaguely restless, and apparently it was sufficient for me to, many years later, have (prompted by an egregious accessibility fail that reminded me of another logic puzzle about lightbulbs) come up with a few more answers:

Answer 1 presumes that the householder is working alone. Answer 2 recruits one or more of the householder's family, housemates, or friends, who communicate the rough time to the householder while the householder is at one of the other clocks, and then an exact time mark when the master clock strikes the second. This does assume the householder (or at least one of the assistants) can hear; delays in reaction time and for sound propagation can be compensated for with preparation (shout the mark a certain amount *before* the actual mark).

Answers 1 and 2 presume that the householder must synchronize all clocks within a relatively short span of time. Answer 3 allows the householder to work alone provided the grandfather clock's chimes work, and that the householder can hear the chimes at all locations within the house. The householder waits until a short time before the grandfather clock will chime, ascertains what the time will be at the moment of chiming, and waits in readiness by each clock to be synchronized in turn. The synchronization will take several iterations that depend on the frequency of the grandfather clock's chimes before they are all complete.

Answers 1-3 presume that the other household clocks are in fact immobile. Answer 4 presumes that they are mobile. The householder fetches each lesser clock in turn, and sets them in front of the grandfather clock before returning them to their stations.

Answers 1-3 presume that the householder or assistants can hear. Answer 5 does not, and may allow for immobile lesser clocks. The householder's assistants position themselves by the lesser clocks on the summer Solstice and watch for the hour of noon themselves.

Answers 1-5 presume that anyone even cares about the lesser clocks being synchronized to within a few minutes of error. Answer 6 declares that no one does and flounces off to do something more interesting.

Comments

[cxcvi]

Answer 6 declares that no one does and flounces off to do something more interesting.

Such as making an antique clock automatically synchronize itself using a radio time signal (not sure which ones operate in your area, but over here, it would probably either be The Time from NPL or DCF77; Wikipedia suggests that WWVB would be the likely choice over there) so that you never have to worry about the clocks being the wrong time again?

[azurelunatic]

That is an excellent more-interesting thing. :D

[cxcvi]

And answer number 7, perhaps?

[cme]

I'm with answer 6! :)

[azurelunatic]

I tend to be too.

[musyc]

Not a single one of my clocks says the same time as any other. My bedroom clock is thirty minutes into the future. My wristwatch is accurate for time, but lives two days in the past. The microwave, stove, CD player, and TV are all 1-2 minutes off from each other. I don't think any clock except the computer is accurate to "proper" time. So I'm going to go with answer six. XD

[azurelunatic]

I often keep my stove clock at GMT -7 all year, since that's where my best friend is. The bathroom clock is mostly useful for relative times, "woops, I've been in the shower 20 minutes!!!" and the computer clock and the cellphone clock are the important ones. Though I tend to set everything from the alarm clock, because it can be seen in all corners of the apartment.

[krait]

Heh. My car clock is still in a different time zone, either because I am the laziest sod on earth or because I secretly resent having to leave said time zone. :D

(My alarm is set somewhere between 4 and 9 minutes ahead -- too little time to justify sleeping more when I look at it, but enough to give me a few extra minutes in case of emergencies. Ideally, I am not entirely certain of the exact number of minutes ahead it has; but this isn't always possible to achieve.)

[exor674]

Hah, my phone, desktop, and laptop all have the correct time.

My alarm clock is close enough to wake me up.
My thermostat once had the correct time, but DST changes and the fact that it's clock isn't perfect has caused it to drift a lot.
My microwave oven clock has never been set since the last power failure.
My oven clock would probably still be flashing, except for the fact that I have to set it to use the oven ( so it shows some random time, most likely using the time of the last power failure as "midnight" )

<_<

[flyingthesky]

but couldn't all the "lesser" clocks be atomic clocks and therefore perpetually kept in time by downloading the correct time from whatever nearest atomic clock?

or am I to presume that these clocks must all be manually set, which seems a little silly to me. All of my clocks set automatically, except the one in the bedroom which is only powered because I need noise to go to sleep.

[azurelunatic]

The original question was posed to me in the late 1980s, so the original setup did not even conceive of networked time.

But these days, yes.

[pauamma]

NTP version 3 was defined in 1992, so an earlier version might have existed in the late 80s - probably not generally known then, though.

[drewkitty]

Answer 8: set all clocks from my network-sync mobile phone.

[krait]

The Fer-De-Lance answer presupposes that the clocks are within a house with a working telephone. The clock owner calls the Correct Time number while standing in front of each clock and sets it accordingly, on any day that is convenient. (The call would have to be set up and the clock prepared for setting such that the clock may be set as soon as the correct time is announced; this would probably entail dialing first and opening the clock while the phone rings.)

[krait]

Bonus, after having read the comments: I'm pretty sure that the Correct Time phone number thing existed even in the 80s, though I'm not completely certain. *ponders how to research this*

[azurelunatic]

My father used the university's atomic clock phone number a lot. For a while I had it memorized. So yes, it existed then.

[krait]

Huzzah!

(Because I like my silly headgame puzzles to be historically accurate!)

[pne]

Slight correction: this answer seems to presuppose that the clocks are within a house with a working *cordless* telephone.

Or, alternatively, a telephone with a cord long enough that it can be carried into any room in the house; or mobile secondary clocks; or a telephone in every room that has a clock.

[krait]

I was thinking "a telephone within reach of each room with a phone", since I remember my childhood-in-the-80s/90s household had some phones with very long cords. :D

It could, however, be combined with azurelunatic's "the clocks can be carried" answer, in the case of some rooms not being within reach of the telephone...

[krait]

The second Fer-De-Lance answer presupposes that the clock owner is in possession of a couple of decent nights' sleep and a reasonable quantity of caffeine, sufficient to ensure concentration is not impaired. It will also require a few training/practice sessions before the solstice.

The clock owner sets the grandfather clock at the solstice, and then proceeds to count seconds while walking to the next clock, which is then set to the correct time; the clock owner then counts seconds while walking to the third clock, sets it, and so on.

[jeshyr]

Ohh!

Music!

Clock owner could totally put on some music that was close enough to 60bpm or 120bpm to assist with the above!

[arkeiryn]

I don't see what's wrong with answer 1 :/

[azurelunatic]

Nothing wrong, really, it just did not involve twisting my brain enough. It felt too easy.

[pauamma]

1- Memorize time on grandfather clock, t0
2- Walk to other clock
3- Memorize the time on other clock, t1
4- Go through the motions of adjusting other clock (open/close glass cover or whatever) without actually changing the time
5- Memorise the new time on other clock, t2
6- Walk back to grandfather clock
7- Note the new time on the grandfather clock, t3
8- Return to other clock, and set it to t3 + (t3 - t0) / 2 - (t2 - t1) / 2

[pne]

Slightly related - this reminds me of the story by (I believe) Corrie ten Boom.

Where she described how her father (I think it was) was proud of having a clock that showed the exact time, and once a year he would carry it to Amsterdam to set it from the big clock there, and during the year, people in his village would occasionally come to him to set their clocks from his.

Then, as the years went on, fewer and fewer people came because clocks and watches that kept good time (and didn't need to be set regularly) became more easily available.

[jeshyr]

Assuming that setting Mobile Clock from Master Clock and then lesser clocks from mobile clock is sufficiently accurate for the purpose, Answer 4 actually only needs one clock in the house to be mobile.

This brain exercise made me very happy :)

[tsjafo.livejournal.com]

I like answer 3.

[jd]

Huh, to me answer 1 is so patently obvious that it doesn't even approach being a puzzle. I spent a few minutes looking at it going "surely there must be more to it than that".

But how does answer 1 presume hearing?

[azurelunatic]

... you're right, it doesn't.

I am pretty sure I was in elementary school when we got this question, and I think the thing that we were meant to learn is that sometimes the answer to a thing involves introducing a new element not mentioned in the setup.

[jd]

Ah, that framing makes a bit more sense, then. I think also it seemed a bit odd to me because I remember reading Lateral Thinking puzzle books (and Encyclopedia Brown, which is another matter entirely) towards the end of that age bracket and found them fiendishly difficult. But I think it was good in a mental development sense.