Day Date clocks

[Mick F]

Our battery driven kitchen clock high up in the wall has a day and date. It's unintelligent and every month has 31days as far as it's concerned.

I (eventually) lifted it down yesterday and put the date right. It was a date out as I hadn't altered it at the beginning of July. The day is always correct of course, but as the months have different numbers of days, it tends to need the date altering every month or so.

Question:
The day and date were correct on Jan 1st this year. It was a Tuesday, and if I hadn't altered the date at the start of March, when would the day and date be correct again?

My brain hurts trying to work it out!

[661-Pete]

If it isn't a leap year, then you can re-use the same calendar after either 6 or 11 years, depending on how many leap years intervene. In this case, you can use the 2019 calendar again in 2030.

If it's a leap year, you'll have to wait 28 years. The situation will be different as we approach the year 2100 (which isn't a leap year).

[Mick F]

If it isn't a leap year, then you can re-use the same calendar after either 6 or 11 years, depending on how many leap years intervene. In this case, you can use the 2019 calendar again in 2030.

If it's a leap year, you'll have to wait 28 years. The situation will be different as we approach the year 2100 (which isn't a leap year).

Thanks for that, but will 2100 not be a leap year?

The rule is, that leap years happen when the year is divisible by four, but not divisible by one hundred.
That would have made Y2K a non-leap year, but it actually was. They make the rules up as they go along.

I don't think that our clock will still be running in 2030.

[661-Pete]

The Gregorian calendar ordains that if a year is divisible by 4 but not by 100, it is a leap year.
If a year is divisible by 100 but not by 400, it is not a leap year.
If a year is divisible by 400, it is a leap year.
Hence 2000 was a leap year, as will 2400, 2800 etc. 2100, 2200 and 2300 will not be leap years.

It occurs to me that anyone born on 29 Feb 2000, won't have the pleasure of the telegram* from whoever's succeeded to 'er Maj, on their 100th birthday - because they won't have a 100th birthday! Poor devils - I can only sympathise...

*Actually it's not a telegram anymore - it's just a birthday card 'signed' by E2R. But it's still scheduled to arrive on the big day...

[Mick F]

You have to request it.
It's not automatic.
Neighbour turned 100 a few years ago. His son had to request the card from Buck House plus submit proof of his dad's age.

That's for putting me right re 400years. That's why it wasn't a LY in Y2K! I thought it was something to do with a correction.

I'm not sure that the battery in our kitchen clock will still have any charge left in it by 2030 BTW.

[merseymouth]

Hi all, For me the best clock or watch just tells the time - nothing else!
My Watts of Derby open face pocket watch "Tics" all the boxes, old as well, I don't want to be "Fobbed Off" with modern rubbish. One of my fobs is made from the copper cladding from HMS Victory, truely copper bottomed! TTFN MM

[iandriver]

My favourite clock is the one in my weather station with additional outdoor sensor. Updates itself. The amount of times the family now announces the temperature, including the decimal point, is hilarious.

Must try to find one with a wind speed and direction facility.

[River_rat]

OK, I'm bored, waiting to go and pickup my £16.11 ebay special.

In reply to the original question: It'll be right again in Dec (and still right the following Jan/Feb).
Month Days Days<31 Running total
Jan 31 0 0
Feb 28 3 3
Mar 31 0 3
Apr 30 1 4
May 31 0 4
June 30 1 5
July 31 0 5
Aug 31 0 5
Sept 30 1 6
Oct 31 0 6
Nov 30 1 7
Dec 31 0 7
Of course if it's a leap year it goes out by 1 day, so you'll then have to wait for 7 leap years for it to be right again.

RR

[Mick F]

That can't be right.
If it's Tuesday 1st Jan 2019, and all the midnights come and make the day correct for the mornings, the days will remain correct permanently.
The issue came at the beginning of March 2019. It would say the 1st on the 4th of March because of 28days in February.
The 1st would show 29th
the 2nd would show 30th
the 3rd would show 31st
..... and the 4th would show the 1st.
March has 31days, so it wouldn't show the 1st of April until the 4th

30days hath September, April, June, and November.
All the rest hath 31 except Feb ...............

My brain is still hurting. I need some more beer.

[kwackers]

30days hath September, April, June, and November.
All the rest hath 31 except Feb ...............

My brain is still hurting. I need some more beer.

So for Sept, Apr, Jun & Nov you shift forward 4 days. On none leap years you also shift forward 3 for Feb (or 2 if a leap).
So advance 7 days in a none leap year and 6 in a leap year.

In March you're out by +3 days (1st = 4th)
Mar 2020 +3+6 = 9 days (1st = 10th) *leap year
Mar 2021 +9+7 = 16 (1st = 17th)
Mar 2022 +16 + 7 = 23 (1st = 24th)
Mar 2023 + 23 + 7 = 30 (1st = 31st)

So nearly there, just need one day which will happen at the end of April.
So 1st May 2023 is the next time it'll be correct.

I think.

[philvantwo]

You need one of those round brass calenders Mick F, the sort you see in the souvenir tat shops down in Cornwall. They tell you all dates for 500 years!

[Mick F]

Glass of red wine has sorted it for this year.

Tuesday 1st Jan 2019 and the clock was correct.
If I did nothing - other than maybe change the AA battery - on 31st December it would also be a Tuesday, but the clock would say the date would be the 24th.

Extrapolate that - but I may need more wine - that the clock would be seven days late per year, so it would take six(?) years to be correct, or five years if a leap year is involved.



Scottish joke:
Is that a cake, or a meringue?

[kwackers]

Oh, the day has to be right as well...

You're on your own then. It's gone 9:30 which is my bedtime and I've already used today's quota of grey matter.

[Mick F]

Oh, the day has to be right as well...

That's what I've been saying!

Good morning BTW.

The clock has the date and the day. That's all. No month involved.
The day is always correct as all weeks have seven days in them. Set it correct, and it remains so.

The issue is that the clock only sees 31days before it resets to the 1st. You can manually correct it of course.
As each month passes, the date is further and further wrong unless you manually correct it.

When will it be right again without any manual input? .............. before being wrong again in the next month or so.

[kwackers]

When will it be right again without any manual input? .............. before being wrong again in the next month or so.

I reckon my calcs above are right.

1st May 2023 is the next time it'll be right.