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  1. #16
    Join Date
    Oct 2010
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    Canberra
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    Re: cal for year 1700 is in error

    OK, lets consider the case of an historical document written on Christmas day in 1750 in London, England.
    The date on that document would be (according to cal): Tuesday, 25 Dec 1750.

    Are you suggesting that such a real letter would have something different, because I cannot see how that would be the case. ?

  2. #17
    Join Date
    Nov 2008
    Posts
    324

    Re: cal for year 1700 is in error

    As per the explanation at http://aa.usno.navy.mil/data/docs/JulianDate.php, since England and colonies did not adopt the Gregorian calendar until
    September 1752, in 1700 they were still under the Julian calendar (leap year every 4th year), which means 1700 would have been a leap year, so cal is correct (unless you live in Italy ...).

  3. #18
    Join Date
    Jun 2005
    Location
    Montreal, Que, Canada
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    4,482

    Re: cal for year 1700 is in error

    From my code and from what was written up as an ISO standard, perhaps it's time for cal to be reviewed. I am attaching three documents
    8601v2000.pdf ISO Standard
    JulianDateExplanation.odt (libreoffice doc from Dr Dobbs Journal, by Peter Meyers. A very interesting read)
    with code that matches Stanford Univ, and other sites.

    weekiso.doc for some code that may be of interest to you

    The importance of date routines is mainly for calculations for dates and finance
    daysapart day1 to day2
    workingDays between day1 to day2
    Day of the week for a date
    Manufacturing Calendars for production planning. (Many manufacturing calendars use a modulo 1000 day planning cycle).
    Attached Files Attached Files
    Leslie in Montreal

    Interesting web sites list
    http://forums.fedoraforum.org/showth...40#post1697840

  4. #19
    Join Date
    Oct 2010
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    Canberra
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    Re: cal for year 1700 is in error

    Your examples for the use involves the future or the recent past - several hundred years ago seems a bit out of range.

    The only practical purpose I can see for a calendar program going back into history is to determine what day of the week certain events happened on. In such a case the location is also an important factor since countries changed calendars at different times.

    I've had a quick look at the documents you attached. I cannot see anything which convinces me that cal needs to be modified. Perhaps an option to specify the change over date, but otherwise it seems an entirely reasonable solution for what it does.

    Please do not insist that it is wrong - it is correct for Britain and its colonies.

  5. #20
    Join Date
    Feb 2011
    Posts
    170

    Re: cal for year 1700 is in error

    England and colonies did not adopt the Gregorian calendar until
    September 1752, in 1700 they were still under the Julian calendar (leap year every 4th year), which means 1700 would have been a leap year, so cal is correct (unless you live in Italy ...).
    and unless you live in Montreal, which was not an English colony in 1700...

  6. #21
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    Jun 2005
    Location
    Montreal, Que, Canada
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    4,482

    Re: cal for year 1700 is in error

    Interesting converter from calendar day to Julian. Try 1700 2 29
    Leslie in Montreal

    Interesting web sites list
    http://forums.fedoraforum.org/showth...40#post1697840

  7. #22
    Join Date
    Jun 2005
    Location
    Montreal, Que, Canada
    Posts
    4,482

    Re: cal for year 1700 is in error

    Well, my bug with Cal has been verified as follows:

    date --date="1700-01-01 + 59 days" output:
    Mon Mar 1 00:00:00 LMT 1700

    date --date="1700-01-01 + 58 days" output:
    Sun Feb 28 00:00:00 LMT 1700

    So date and cal are inconsistent.
    ("date" from coreutils-8.27-6.fc26.x86_64)
    Leslie in Montreal

    Interesting web sites list
    http://forums.fedoraforum.org/showth...40#post1697840

  8. #23
    Join Date
    Nov 2008
    Posts
    324

    Re: cal for year 1700 is in error

    The Modified Julian Date, which is the number of days since 1 Jan 4713 B.C., is used by astronomers, and sometimes historians. If "cal" and/or "date" are being considered for enhancement / correction, the "--MJD" option might be considered too. Ref: https://bowie.gsfc.nasa.gov/time/

  9. #24
    Join Date
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    Re: cal for year 1700 is in error

    Of course they are inconsistent.
    date, based on the content of its man page, uses ISO 8601as its reference, and ISO 8601 uses the Gregorian calendar starting in 1582.
    cal uses the Gregorian calendar, but starting in 1752, when it was adopted by Britain and its colonies (which includes the USA).

    Both are correct relative to their specifications.

    Anyone trying to do actual historical work should be aware that the calendars were adopted at several different times in different places and make the appropriate allowances. For example, there was a time when someone could get a letter in London that was written in Paris with a date on it that was in the future according to the English calendar.

    Trying to use software outside of its specified limits is always going to problematic. Its up to us as users to understand those limits and make the appropriate adjustments.

    If I were to make any change to the software (cal, date, etc.) it would be to add an option that allowed the user to specify when the Gregorian calendar was adopted.

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