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Insane complexity of calendrically correct date and time operations

yourcalendricalfallacyis.com

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Re: Insane complexity of calendrically correct date and time operations

#131

Post by macintux »

Tor3 wrote: post #101
thaumasiotes wrote: post #95

Earlier quoted context omitted.

In the US, weeks are not numbered, and the way to refer to a week is e.g. "the week of the 10th". (If you're talking about a different month, "the week of September 10th".) You would usually name the Monday of the week because the context is usually work-related. I question whether "Thursday of week 37" is really that much clearer than "Thursday, September 13".

Indeed, it isn't. I'm living in a country where my company as well as our (foreign) customers use week numbers all the time. It's painful. My watch doesn't show the week number. A normal calendar doesn't. The company calendars do, but there's never one nearby when I need one. So I have a bookmark in my web browser to a 'week calendar' on the net. I can use a 'date' command, but the actual +% syntax always disappear f…

I wrote a date parsing library and spent a fair bit of time trying to wrap my brain around week numbers. Definitely messy.

It never occurred to me to check my Apple Watch for a week number complication. A bit disappointed it's not there, even if I'd never use it.

Update: you can install an app to Apple Watch that supplies a complication for it. "Current Week".

Re: Insane complexity of calendrically correct date and time operations

#132

Post by TomK32 »

drtillberg wrote: post #28

Christ Church College at Oxford still makes a limited use of 'local time' offset 5 minutes and 2 seconds from the time zone. https://greenwichmeantime.com/info/oxford/

Jolly good, the whole rail-road mania with their cum tempore timetables never full-filled their fantasy of a unified time-zone for Old Blighty.

Re: Insane complexity of calendrically correct date and time operations

#133

Post by Spivak »

WalterBright wrote: post #69

This really should be an operating system service, so all the applications get it right. Instead, everybody rolls their own, with erratic results.

Android: https://developer.android.com/reference/android/icu/util/Cal...

Apple Everything: https://developer.apple.com/documentation/foundation/nscalen...

CentOS: https://centos.pkgs.org/7/centos-x86_64/icu-50.1.2-15.el7.x8...

Windows: https://docs.microsoft.com/en-us/windows/desktop/intl/intern...

Re: Insane complexity of calendrically correct date and time operations

#134

Post by WalterBright »

Spivak wrote: post #133
WalterBright wrote: post #69

This really should be an operating system service, so all the applications get it right. Instead, everybody rolls their own, with erratic results.

Android: https://developer.android.com/reference/android/icu/util/Cal... Apple Everything: https://developer.apple.com/documentation/foundation/nscalen... CentOS: https://centos.pkgs.org/7/centos-x86_64/icu-50.1.2-15.el7.x8... Windows: https://docs.microsoft.com/en-us/windows/desktop/intl/intern...

Only Microsoft's seems to be part of the operating system.

Re: Insane complexity of calendrically correct date and time operations

#135

Post by disillusion »

AllegedAlec wrote: post #90
netgusto wrote: post #74

> Weeks start on Sunday in the United States, Monday in Europe, and a couple of places start on Saturday. Wow. I live in Europe, and find it weird that people can consider the week to start on Sunday. I guess everything that may appear normal within a cultural frame of reference can be off in another, even the most basic of things!

> Wow. I live in Europe, and find it weird that people can consider the week to start on Sunday. Netherlands reporting in. My parents always taught me that the week starts on Sunday.

Funny, I'm Dutch and I learned the week starts on Monday. Well, except for strongly religious families.

Re: Insane complexity of calendrically correct date and time operations

#136

Post by ardy42 »

svckr wrote: post #106
netgusto wrote: post #74

> Weeks start on Sunday in the United States, Monday in Europe, and a couple of places start on Saturday. Wow. I live in Europe, and find it weird that people can consider the week to start on Sunday. I guess everything that may appear normal within a cultural frame of reference can be off in another, even the most basic of things!

I mean … I was aware of the fact that the week starts on Sunday in a LOT of other places. But still. So Sunday, the first day of the week, is still part of what's called the weekend, right?

> I mean … I was aware of the fact that the week starts on Sunday in a LOT of other places. But still.

> So Sunday, the first day of the week, is still part of what's called the weekend, right?

I've always interpreted "the weekend" as a shortening of "the weekends." Sunday is at one "end" of the week and Saturday is at the other "end." Sort of like a if you hold a stick out, there's a "near end" and "far end."

Re: Insane complexity of calendrically correct date and time operations

#137

Post by repolfx »

bloak wrote: post #120
repolfx wrote: post #117

Earlier quoted context omitted.

But offset of UTC for TAI is like 37 seconds or something poxy like that. Nobody cares about this, the sun moves too slowly for that to make any difference. There's been talk of setting UTC=TAI for quite a long time and I think it'd make sense. It'd take so long for TAI to drift from the actual rising and setting of the sun that we'd probably all have standardised on Swatch Beats by then anyway.

Yes, the difference is 37 seconds now, but it's growing quadratically. It's quite possible that we'll change the way we express times and dates, but it's almost certain that we'll want them to stay in phase with the sun, and we'll probably want to stick with the SI second and with something like TAI. My guess is we'll continue to want a simple relationship between TAI (or its successor) and the civil clock time, some…

What do you mean by growing quadratically, exactly? The rotational drift of the Earth is growing that fast? Where can I read more about this?

Re: Insane complexity of calendrically correct date and time operations

#138

Post by bloak »

repolfx wrote: post #137
bloak wrote: post #120

Earlier quoted context omitted.

Yes, the difference is 37 seconds now, but it's growing quadratically. It's quite possible that we'll change the way we express times and dates, but it's almost certain that we'll want them to stay in phase with the sun, and we'll probably want to stick with the SI second and with something like TAI. My guess is we'll continue to want a simple relationship between TAI (or its successor) and the civil clock time, some…

What do you mean by growing quadratically, exactly? The rotational drift of the Earth is growing that fast? Where can I read more about this?

The length of the day is increasing roughly linearly at roughly 2 ms (per day) per century, because of tidal effects. The difference between TAI and UT1 is the integral of that, so grows quadratically. If we assume that the mean solar day was "correct" around 1900, then a hypothetical atomic clock that was synchronised to the sun around 1900 is, after x centuries, out by about 36525.x^2 ms. TAI was in fact synchronised to UTC around 1960, when atomic clocks were widely used, and the slowing down of the Earth's rotation is rather unpredictable in the short term (decades), perhaps being affected by climate change, so the numbers are all imprecise, but the long-term (centuries, millennia) quadratic growth of the TAI-UT1 difference is inevitable.

Re: Insane complexity of calendrically correct date and time operations

#139

Post by guan »

jchw wrote: post #7

Many of these make the weird assumption that you want to support multiple calendars. For better or worse, this is rarely the case.

That was my thought reading this list too. I am sure every calendar system will have a list of calendrical fallacies like this. But if you do decide to support the Hebrew calendar, you will not get “The current year is 2018” wrong. Or the number of digits in a year, if you choose to support the Japanese calendar. Actual fallacies in those systems will be less obvious.

Re: Insane complexity of calendrically correct date and time operations

#140

Post by sla29970 »

bloak wrote: post #138
repolfx wrote: post #137

Earlier quoted context omitted.

What do you mean by growing quadratically, exactly? The rotational drift of the Earth is growing that fast? Where can I read more about this?

The length of the day is increasing roughly linearly at roughly 2 ms (per day) per century, because of tidal effects. The difference between TAI and UT1 is the integral of that, so grows quadratically. If we assume that the mean solar day was "correct" around 1900, then a hypothetical atomic clock that was synchronised to the sun around 1900 is, after x centuries, out by about 36525.x^2 ms. TAI was in fact synchronis…

Yes, roughly quadratic increase of LOD over the long term, but over short term more like a random walk. Right now the earth's crust is rotating faster than it did a century ago because things have speeded up. For a view over 2 millennia see plots of LOD at https://www.ucolick.org/~sla/leapsecs/dutc.html
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