Calendar Functions for dates starting in 1582
11-14-2021, 07:46 PM
Post: #1
 Matt Agajanian Senior Member Posts: 947 Joined: Dec 2013
Calendar Functions for dates starting in 1582
Hi all.

Pretty much the majority of calendar functions programs for HP-67/97 start with the year 1900.

Are there calendar function programs which work with dates as early as 1582?

Also, is there an algorithm for the 67/97 which calculates a date + or - from date on or after 1582?

Thanks
11-14-2021, 08:30 PM (This post was last modified: 11-14-2021 08:32 PM by Maximilian Hohmann.)
Post: #2
 Maximilian Hohmann Senior Member Posts: 1,188 Joined: Dec 2013
RE: Calendar Functions for dates starting in 1582
Hello!

Look no fiurther than here: https://literature.hpcalc.org/community/...endars.pdf
(On page 30 you will find the answer to question 2, question 1 is answered by pretty much all pages in that document.)

Regards
Max
11-19-2021, 04:58 AM
Post: #3
 Matt Agajanian Senior Member Posts: 947 Joined: Dec 2013
RE: Calendar Functions for dates starting in 1582
Brilliant!!

Thanks!!
11-19-2021, 01:18 PM
Post: #4
 Albert Chan Senior Member Posts: 2,356 Joined: Jul 2018
RE: Calendar Functions for dates starting in 1582
Only 1 calendar needed ... Calculators calendar of 1974

11-19-2021, 10:54 PM
Post: #5
 Archilog Member Posts: 107 Joined: Dec 2013
RE: Calendar Functions for dates starting in 1582
(11-19-2021 04:58 AM)Matt Agajanian Wrote:  Brilliant!!

Thanks!!

Twice is better than never: many thanks.
11-22-2021, 02:43 PM
Post: #6
 aamiel Junior Member Posts: 17 Joined: Apr 2017
RE: Calendar Functions for dates starting in 1582
Be careful when using 1582 blindly. In most cases it is the wrong year.
12-14-2021, 11:20 PM
Post: #7
 Matt Agajanian Senior Member Posts: 947 Joined: Dec 2013
RE: Calendar Functions for dates starting in 1582
Hi. Thanks for the User Solutions Calendars link.

Quite useful. Although the date +/- days works with March 1, 1901-Feb 28, 2100, I need to calculate future/past dates starting with 1582. I’ve tried to simply add the amount of days plus/minus to the generated Julian/Gregorian Date Number, but that doesn’t work.

Could you help me with that, please?

I found this on the web, but it doesn’t include date arithmetic formulas.
Julian/Gregorian Date Numbers

Thanks
12-15-2021, 12:09 AM
Post: #8
 Albert Chan Senior Member Posts: 2,356 Joined: Jul 2018
RE: Calendar Functions for dates starting in 1582
(12-14-2021 11:20 PM)Matt Agajanian Wrote:  Although the date +/- days works with March 1, 1901-Feb 28, 2100, I need to calculate future/past dates starting with 1582. I’ve tried to simply add the amount of days plus/minus to the generated Julian/Gregorian Date Number, but that doesn’t work.

Greogrian calendar repeat itself, every 400 years = 365.2425 * 400 = 146,097 days
Within the 400 years, as long as we do not cross years divisible by 400, 1 century = 36524 days

We can thus "pull" any dates to within working range of Mar 1,1901 - Feb 28, 2100

﻿ ﻿ ﻿ JDN(1/1/1983)
= JDN(1/1/1883) + 36524
= JDN(1/1/1783) + 36524*2
= JDN(1/1/1683) + 36524*3
= JDN(1/1/1583) + 146097
12-15-2021, 10:45 PM
Post: #9
 Matt Agajanian Senior Member Posts: 947 Joined: Dec 2013
RE: Calendar Functions for dates starting in 1582
Hi again, MoHPC compadres.

It all works now!

Thanks for the advice.

I’m working on an HP-67 version.
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