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Re: Decimal time support in 'date'

From: za3k
Subject: Re: Decimal time support in 'date'
Date: Fri, 13 Dec 2019 14:04:40 -0800
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On 2019-12-13 01:03, Assaf Gordon wrote:

Thank you for the suggestion and for checking in first - that's an
excellent approach.

Thanks! And thanks for the reply.

I'm just some guy who wants to write my journal / system clock / etc in this format, I don't use it professionally. That said, I do think it's important to support the actual use cases, so I did a day or two of research. I really need to talk to the people that actually use this stuff to answer many questions :). But I figured there was a good chance coreutils would say 'naaah, no chance' so though I'd check in first.

This is an interesting idea, certainly worth discussing.
When such format is used by time-keepers or scientific recording, is
it being used
on the command-line or from a shell script? or is this more commonly
done in a higher-level programming language?
Can you expand on the other format used by Astronomers?

I basically don't know as to the state of software, although I have educated guesses (timekeeping will use high level languages, but perl CGI scripts will call date--scientific recording will use a mix). The documentation I've found has been about doing it by hand, but that's not much of a hint whether it's normally done by hand. I doubt consulting someone will help answer this, but if can think of anyone, you can put us in touch or ask.

Based on very cursory research, astronomers have multiple systems in active use. They all deviate from the "usual" calendar. Astronomers would need a whole new 'date' specialized for astronomy. I've seeing some Julian dates as a continuous count of days since 4712BC (Julian Date) or another epoch (Modified Julian Date), some using a Gregorian calendar (more uniform leap days) or modified Gregorian calendar. The decimal time part of what they're doing is otherwise the same. Some systems (Julian Date) take solar noon as the start of the day rather than midnight, but I'm not clear whether it's in use.

It's worth mentioning for the curious that a decimal time system is used by "Internet Time" (some Swiss watchmaker's gimmick? -- again no DST is observed) and has been used historically. Notably, for 2-3 years after the French Revolution nation-wide (again no DST is observed), which I think is why it's relatively standardized; this was how the metric system was formed but decimal time had poor adoption. Wikipedia claims decimal time may have been used historically in China but I'm not personally familiar enough.

Again, NONE of the systems seems to be widely adopted (decimal hour and day DURATIONS are widely adopted in timekeeping for daily/hourly workers, but that's different). The reason I'm proposing the decimal portion of the day to X digits is that it seems to be the part that's consistent across all of these systems, and it's enough to display times in the modern ones. The French system needs substring support to display times like "1:34:56", so if you want to write your dates in 1794 France, you'll have to do your own string postprocessing.

After talking to an expert, there may be some use for decimal fractions of an hour in timekeeping, I'll have to check.

If we consider adding a new letter operator (e.g. "%X" ) we should
make sure it does not conflate with any existing letters, including on
non-gnu implementations (e.g. on BSDs).

Good reminder. Other than GNU and BSD ports, any specific implementations to check?


On 2019-12-12 21:53, Kenneth Irving wrote:
I've been using the 'decimal day' informally for my own purposes for
several years, and used to have a widget display it along with
'regular' time on my workstation.


I'm not sure how either of these would work out in coreutils date(1),
since it has to take a more formally correct approach, but perhaps
they could be useful.


Well I'm glad to hear at least one person would use this. In general I would prefer to add only format types which would be used by several people and preferably are relatively standardized--I'm happy to play with time systems on my desktop widgets etc but I need a justification to add stuff to coreutils :) I haven't seen anyone else use decimal years, although it does seem like a perfectly sensible system.

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