Chron Time

TypeScript implementation of Chron Time, a calendar date and time-of-day notation that keeps the Gregorian year and leap rule, writes the year as 26 fortnights plus Year Day and Leap Day, divides the day into 1000 chrons, and uses a longitude zone whose sign adds toward GMT.

npm install @chrontime/chrontime

import {
  parse,
  ChronInstant,
  ChronDate,
  ChronTime,
  ChronDuration,
  fromUtc,
  fromRfc3339,
  zoneFromLongitude,
} from '@chrontime/chrontime';

ChronInstant.parse('2026R04:659.472+269').toCanonical();
// '2026R04:928.472Z'

fromUtc(new Date('2020-02-09T12:00:00Z')).toCanonical();
// '2020C12:500Z'

ChronDate.parse('2026R4').toGregorian();
// { year: 2026, month: 8, day: 30 }

ChronTime.parse('200+300').equals(ChronTime.parse('500Z'));
// true

ChronDuration.parse('0.050d').toCanonical();
// '50c'

zoneFromLongitude(96.9); // Carrollton, Texas, west longitude
// 269

Calendar

The year number and leap rule are Gregorian. Day 1 of fortnight A (A01) is 1 January.

Slot	Days of year	Notes
Fortnights A–Z	1–364	14 days each
Year Day YD	365	not in a fortnight, month, or week
Leap Day LD	366	leap years only; Gregorian 29 February is an ordinary Chron day (2020E04)

A common year ends Z14, YD. A leap year ends Z14, YD, LD.

There are 13 months of two fortnights (28 days). The written date uses the fortnight letter, not a month number.

Time of day

A day is 1000 chrons. Chron 000 is midnight UTC. Chron 500 is noon UTC. One chron is 86.4 POSIX seconds.

Chron Time uses the POSIX scale: every calendar day is 86400 seconds. A leap second is not a distinct Chron instant. RFC 3339 23:59:60 maps to chron 999 of that UTC date, never to 000 of the next day.

Zones

A zone is a longitude band, not a civil time zone. Daylight saving and other clock laws do not change it.

local + zone = GMT

West of Greenwich is plus. East is minus. Z means zone +000.

2020C12:200+300   // local 200 at 108°W
2020C12:500Z      // the same instant

Chron-resolution zone from west longitude:

zone = round(longitude_west_degrees / 0.36)

The 180th meridian is +500. -500 is not written. Implementations that ingest both Chron Time and ISO 8601 must not reuse an ISO offset parser for a Chron zone.

Profiles

Profile	Use	Instant example
Presentation	people	2026R4:659 (day padding and zone may be omitted)
Interchange	storage and transmission	2026R04:659.472+269 (padded fields, zone required)
Canonical	equality	2026R04:928.472Z (reduced to GMT, quantum applied)

Two values of the same kind are equal if and only if their canonical strings are identical.

Canonical numeric fields round to 0.001 chron using half-away-from-zero. Trailing zeros are stripped (720.000Z → 720Z). If time rounds to 1000, it carries into the next Chron day.

An omitted zone is allowed only in presentation. It means the local meridian is understood. It is not GMT. A date-only string names a calendar day, not an instant.

Parsing

parse classifies the string:

• c or d unit suffix → duration (50c, 3d200c, -50c)
• contains : → instant
• year then fortnight / YD / LD, no colon → date-only
• otherwise → time-only

parse('2020C12:200+300'); // ChronInstant
parse('2026R04');         // ChronDate
parse('500Z');            // ChronTime
parse('3d200c');          // ChronDuration

Pass { profile: 'interchange' } to reject unpadded days, short years, and missing zones.

Instants

const local = ChronInstant.parse('2026R04:659.472+269');
local.toCanonical();                 // '2026R04:928.472Z'
local.atZone(0).toInterchange();     // '2026R04:928.472Z'
local.toDate().toISOString();        // POSIX UTC from §6

const presentation = ChronInstant.parse('2026R4:659');
presentation.withZone(269).toCanonical();

withZone assigns a meridian to a presentation string. atZone rewrites the same instant at another meridian.

fromUtc / fromRfc3339 convert a JS Date or RFC 3339 timestamp. A civil offset is used only to find the UTC instant; it does not become the Chron zone.

Adding a duration carries through fortnights, Year Day, and Leap Day:

ChronInstant.parse('2020Z14:980Z')
  .add(ChronDuration.parse('50c'))
  .toCanonical();
// '2020YD:030Z'

Development

npm install
npm test
npm run build

The grammar, conversion equations, and worked examples are in the Chron Time spec.