---
title: "Compu-Calendar"
type: "article"
slug: "compu-calendar"
url: "http://localhost/article/compu-calendar/"
markdown_url: "http://localhost/article/compu-calendar.md"
published_at: "2020-10-27T17:11:03+00:00"
modified_at: "2026-06-21T23:37:01+00:00"
featured_image:
  url: "http://localhost/wp-content/uploads/2022/04/20230809-041332.jpg"
excerpt: "This three-part program returns correct day name, changes Gregorian dates to corresponding Julian day numbers, and computes total days between any two dates from Jan. 1 AD to Feb. 2300. To use, type the month number (NL) , day number (NL) , and fourdigit year (NL) . ZX80 returns the correct day name, followed by…"
category:
  - name: "Syntax"
    slug: "syntax"
    taxonomy: "category"
    url: "http://localhost/category/periodicals/syntax/"
post_tag:
  - name: "1980"
    slug: "1980"
    taxonomy: "post_tag"
    url: "http://localhost/tag/1980/"
  - name: "Full Text"
    slug: "fulltext"
    taxonomy: "post_tag"
    url: "http://localhost/tag/fulltext/"
  - name: "Type-in program"
    slug: "type-in-program"
    taxonomy: "post_tag"
    url: "http://localhost/tag/type-in-program/"
  - name: "ZX80"
    slug: "zx80"
    taxonomy: "post_tag"
    url: "http://localhost/tag/zx80/"
model:
  - name: "Sinclair ZX80"
    slug: "zx80"
    taxonomy: "model"
    url: "http://localhost/model/zx80/"
indiv:
  - name: "Otis Imboden"
    slug: "otis-imboden"
    taxonomy: "indiv"
    url: "http://localhost/indiv/otis-imboden/"
publication: "Syntax"
publication_r:
  id: 10246
  title: "Syntax"
  type: "periodical"
  url: "http://localhost/periodical/syntax/"
authors: "Otis Imboden"
authors_r:
  - name: "Otis Imboden"
    slug: "otis-imboden"
    taxonomy: "indiv"
    url: "http://localhost/indiv/otis-imboden/"
volume: "1"
issue: "2"
issues_articles:
  - id: 26692
    title: "Syntax/Syntax ZX80 v1 n2"
    type: "issue"
    url: "http://localhost/issue/syntax-syntax-zx80-v1-n2/"
pages: "5"
pubdate: "December 1980"
archive_link: false
volumeissue: "v1n2"
---

# Compu-Calendar

This three-part program returns correct day name, changes Gregorian dates to corresponding Julian day numbers, and computes total days between any two dates from Jan. 1 AD to Feb. 2300.

To use, type the month number (NL) , day number (NL) , and fourdigit year (NL) . ZX80 returns the correct day name, followed by a prompt. Type J (NL) and it prints the equivalent Julian day number. (Julian days begin at GMT noon on each day and count days from noon, January 1, 4713 BC.)

You can also calculate the number of days between two dates. Enter the earlier one first, using J (NL) to compute JD, then enter the second date but just hit (NL) instead of J (NL) to request total days between the 2 dates.

Note that the ZX80 correctly reads out JD numbers in millions, thousand and units, but blanks leading zeros in each group. When reporting total days, sometimes the program displays thousands of days as 1000 too high, followed by negative hundreds; just add them. For example: A read out of 2,-825 means total days = 1,175.

To exit the program, enter numeral zero (NL) as the month.