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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
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
Brilliant!!

Thanks!!
Only 1 calendar needed ... Calculators calendar of 1974

(11-19-2021 04:58 AM)Matt Agajanian Wrote: [ -> ]Brilliant!!

Thanks!!

Twice is better than never: many thanks.
Be careful when using 1582 blindly. In most cases it is the wrong year.
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
(12-14-2021 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