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      Appendix D: DATECALC, a RAM Resident Date Calculator Utility

      The program DATECALC.COM that has been placed on your Family History
      System program diskette (or in the \FAMILY sub-directory of your hard
      disk) is a program to assist you in performing some standard opera-
      tions involving dates, including:

          Determining the day of the week on which a given date falls;
          Computing the number of years, months and/or days between two
             given dates;
          Determining the date that is a given number of years, months
             and/or days before or after another date;
          Displaying a calendar for the month containing a given date;
          Converting between "old style" and "new style" dates.

      In providing these functions, the DATECALC utility also permits you to
      select the format for dates entered or displayed from among:
              DD MON YYYY   (e.g. 10 APR 1943)
              MON DD, YYYY  (e.g. APR 10, 1943)
              MM-DD-YYYY    (e.g. 04-10-1943)
              DD.MM.YYYY    (e.g. 10.04.1943)
              YYYY MM DD    (e.g. 1943 04 10)
         or   YYYY DDD      (e.g. 1943 100).

      The "difference" or length of interval between dates can be displayed
      in several formats also, including:
               +/- Yr,Mon,Day   (+ 0044 Y  004 M  02 D)
               +/- Yrs,Days     (+ 0044 Y  124 D)
          or   +/- Days         (+ 016195 Days).
      (A "-" before the date difference indicates that the second date
      occurs before the first one.)

      The DATECALC utility can be invoked in several ways.  If you are using
      DOS 3.0 or later and have sufficient RAM on your machine, you should
      be able to invoke it from the MainMenu of the Family History System
      by pressing the F7 key.  It can also be executed as a command from the
      DOS prompt, for example by entering:  A>datecalc
      assuming the DATECALC.COM program is on the diskette in the "A" drive.
      Finally it can be made memory resident by entering:  A>datecalc r
      (again assuming the DATECALC.COM program is on the diskette in the "A"
      drive) after which it may be called up at just about any time by
      simultaneously pressing the ALT and CTRL keys.  The utility will not
      "pop up" when the screen is being used to display graphics and it may
      be incompatible with some other resident utilities or with some
      programs which take control of keyboard input.

      The AUTOEXEC.BAT file created on program diskettes during the standard
      INSTALL procedure has a command line in it which will make this
      utility memory resident when you boot from those diskettes.  If you
      are running from a hard disk or do not boot from your Family History
      System program diskette, you may consider modifying the AUTOEXEC.BAT
      file used during your normal boot procedure to automatically make the
      DATECALC utility RAM resident.  Be aware that making the program
      resident in memory will "permanently" reduce the available memory for
      other programs by about 7k.


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      When you invoke DATECALC in one of the above ways, it "pops" into
      view, overlaying the previous contents of the screen.  The utility's
      options are listed together with the function keys that are used to
      select them.  (Note that the ESCape key is used to exit from the
      program.  The previous contents of the screen are restored when you
      do.)  Below the list of options you will find the descriptions for the
      current formats for DATEs and Date DIFference.  If "old style" dates
      are being processed, then the characters "OS" will appear to the right
      of the literal describing the date format.  Near the bottom of the
      viewing area, on separate lines, appear two dates (DATE1, DATE2) and
      the computed DIF (calendar interval) between the dates.  The day of
      the week for each date is also shown for each date.  The first time
      the utility is used the dates will have the value of the current date
      (or 01 JAN 1980 if you don't have a clock calendar board and haven't
      previously corrected the date using the DOS DATE command or some other
      utility) and the computed DIF will be 0 years, 0 months and 0 days.

      You can use the cursor control keys (as well as the HOME, END, PGUP,
      PGDN keys) to move the viewing area for the utility to different
      locations on the screen.  This allows you to reveal any area on the
      screen in which a date appears that you may want to examine.  If you
      are running DATECALC as a memory resident utility, then the location
      of the viewing area will remain unchanged between separate invocations
      of the program.

      The list of program options appears as follows:
              F1  Enter DATE1 (find DAY)
              F2  Enter DATE2 (find DIF)
              F3  Enter DIF   (find DATE2)
              F4  Show Calendar for DATE1/2
              F5  Change DATE Format/Style
              F6  Change DIF Format
              ESC  Exit

      USING THE DATE CALCULATOR:

      If you press function key F1 or F2 then a reverse video cursor will
      appear in the first position of the value field for the corresponding
      date at the bottom of the viewing area.  You can then type in the
      value you wish and press the Enter or RETURN key when you are through
      (or press the ESCape key to restore the previous value for the date).
      Month literals should be among:
              JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEP,OCT,NOV,DEC
      Any other values entered will be changed to "JAN".  Lower case charac-
      ters are automatically changed to upper case when entering these
      values.  If a value is entered for the day of the month which is
      greater than the "legal" number of days in the month, then the month
      and day (and year if necessary) will be automatically adjusted accor-
      dingly.  For example an entered date of "MAR 35, 1987" will be changed
      to "APR 04, 1987".  Similarly, if a value greater than 12 is entered
      for the number of the month, then the month and year (and day value if
      necessary) will be adusted accordingly.  For example an entered date
      of "14-30-1987" will be changed to "03-01-1988".



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      If you press function key F3 then a reverse video cursor will appear
      in the first position of the value for the DIF field at the bottom of
      the viewing area.  The first character must be a + or - (indicating
      whether the computed value for DATE2 is to be after or before DATE1).
      Press the Enter or RETURN key when you are finished (or press the
      ESCape key to restore the previous value for DIF).

      When entering any of these values you can use the left and right
      cursor control keys to move the cursor and you can use the TAB key to
      move quickly to different parts of the field.  The cursor automatically
      skips over the "filler" characters (such as "-" or ",") so you don't
      have to enter these.

      If you have changed either DATE1 or DATE2, then the program will
      compute and display the day of the week and compute and redisplay the
      value of DIF, the difference between the two dates.  If you change the
      value of DIF, then the program will compute the value of DATE2 which
      is the specified interval before or after the current value of DATE1
      and will compute and redisplay the DIF between the dates.  Note that
      in computing date differences the following procedure is used:
          The larger of the two dates is determined and the sign of the
              difference is set to - if DATE1>DATE2 and + otherwise;
          The smaller date is subtracted from the larger, first days, then
              months and then years.
      On the other hand, when DATE2 is computed from DATE1 the adjustment of
      the components of the date are made in the reverse order, first years,
      then months and then days.  (This is an important distinction and one
      which was not followed by an early version of the DATECALC utility.
      If the components of DATE2 are computed in days, months, years order
      then the computed DIF between DATE1 and the computed DATE2 will some-
      times not match the original DIF value entered.)

      DISPLAYING A MONTHLY CALENDAR

      If you press the F4 key then the middle portion of the viewing area
      for the DATECALC utility will be cleared and a calendar will be
      displayed for the month of the year containing DATE1. (If instead you
      press the SHIFT and F4 keys simultaneously, then the calendar for
      DATE2 will be displayed.)  Once the calendar is displayed, you can
      scroll the calendar backward or forward by months by pressing the left
      or right cursor keys respectively.  The calendar may also be scrolled
      forward or backward by years by pressing the up or down cursor keys
      respectively.  The calendar display is terminated by pressing the
      ESCape key.  (Note: if you are currently using "old style" dates then
      the calendar will be computed using "old style" rules.)

      CHANGING DATE AND DIF FORMATS

      Pressing the F5 key causes the DATEs to cycle through the various
      formats described previously.  Both the literal describing the format
      and the values for DATE1 and DATE2 will automatically change.  All
      dates will be entered and displayed in the currently selected format.

      Similarly, if you press the F6 key then the value for DIF will cycle
      through the various formats described above.  All DIFs will be entered


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      and displayed in the currently selected format.

      If you are running DATECALC as a memory resident utility, then the
      format for DATEs and DIF will be retained between invocations of the
      utility.

      CONVERTING BETWEEN "OLD" AND "NEW" STYLE DATES

      It is generally well known that the "standard" calendar year of 365
      days differs from the "solar" year by an amount that makes it neces-
      sary to insert extra days occasionally (as a 29th day in the month of
      February) to get back in synch with the sun.  The years in which such
      days are added are called "leap years".  The rule for determining leap
      years that has been used in English speaking countries since 1752 (and
      from earlier dates in other enlightened areas of the world...in fact
      the new calendar is called a "Gregorian" calendar after Pope Gregory
      XIII who requested that Catholic countries begin using it in 1582) may
      be stated as follows:
            A given year will be a leap year if it is evenly divisible by 4
            UNLESS the year ends in "00" in which case it is NOT a leap year
            UNLESS it is divisible by 400 in which case it IS a leap year.
      Prior to the establishment of this leap rule, most of the Western
      world employed a rule which was just the first line in the above
      statement, that is every fourth year was a leap year.  The effect of
      using this simplified rule over a long period of time was that the
      planting season, which is determined by the sun, would creep a
      calendar day earlier every 133 years or so.  By the Spring of 1752
      people were having to plant their potatoes the day after Groundhog Day
      instead of Valentine Day.  Therefore to correct the situation all
      English subjects were asked to go to bed the evening of 02 SEP 1752,
      get up the next morning on 14 SEP 1752, and from that day forward use
      the new leap year rule for constructing calendars.

      Today this calendar change is just a curiosity for most of us, but to
      people of that day and genealogists today who have to deal with dates
      both before and after this adjustment it is a problem which has been
      recognised by labeling dates based upon the old leap rule as "old
      style" dates and designating those following the new rule as "new
      style" dates.

      The calendar adjustment to "new style" dates occurred at different
      times in different countries so rather than just treating all dates
      prior to 14 SEP 1752 as "old style" dates, the DATECALC utility pro-
      vides an option for converting between the two "styles".  Pressing the
      SHIFT and F5 keys simultaneously causes the program to shift between
      old and new style treatment of dates with a corresponding adjustment
      of displayed DATEs and DIF values.  When dates are being treated as
      "old style" dates the characters "OS" will appear to the right of the
      literal describing the current Date format.  When the new leap rule is
      in effect there is no special indicator to the right of the Date
      format descriptor (though genealogists will sometimes use an "NS"
      suffix for such dates).

      As an example, call up the DATECALC utility, press F1 and enter the
      new style date: 22 FEB 1732 (or equivalent for the date format you are


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      using).  You will find that George Washington was born on a Friday.
      But if you press F4, the "new style" calendar displayed will not be
      the one that George's parents used to mark his birth.  Instead, press
      ESCape (to erase the calendar display) and then SHIFT+F5 to switch to
      "old style" dates.  You will find that George's birthdate was actually
      11 FEB 1732 (still a Friday though) and if you then press F4 you will
      see the "old style" calendar that was in effect at the time.

      Before ending this discussion, perhaps I should note another distinc-
      tion between some old and new style dates.  Prior to the implementa-
      tion of the new leap rule, the first day of the new year was con-
      sidered variously as Jan 1, Mar 1 and Mar 25 (e.g. according to some,
      25 MAR 1645 was the day after 24 MAR 1644). This left some ambiguity
      concerning the year for such dates as:  11 FEB 1732 OS.  Therefore the
      custom was developed of using "double dating" to take note of the fact
      that this discrepancy had been considered.  The above date might then
      be written:  11 FEB 1731/2 OS.  You should be aware that the DATECALC
      utility will always assume JAN 1 to be the first day of the year.  You
      may even use this to determine the correct double dating for an event.
      For example, suppose it is known that a person was born on Saturday,
      30 JAN 1691 OS, but it is not known which new year rule was in effect.
      The DATECALC program will show that 30 JAN 1691 OS is a Friday but
      that 30 JAN 1692 OS is a Saturday.  Therefore the correct double-
      dating would be:  30 JAN 1691/2 OS and the person who originally
      recorded the date was apparently using something other than JAN 1 as
      the date for the beginning of the new year.


      For those wanting to find out more about various calendar systems I
      would recommend your reading the discussions in the books:
         "Tracing Your ROOTS" by the editors of Consumer Guide and distri-
             buted by Bell Publishing Company, New York  (p. 47)
         "Ancestry's Guide to Research" by Johni Cerny & Arlene Eakle,
             published by Ancestry, Inc., Salt Lake City























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