Chrono 40k

A consistent dating system for "Warhammer 40,000"

If you are not familiar with the imperial dating system in Warhammer 40k please consider to first take a look at https://warhammer40k.fandom.com/wiki/Imperial_Dating_System.

I intentionally diverge from the calculation of the year fraction or chronosegments, more on that in the remark section.

Usage

Installation

Install using npm:

npm i chrono-40k

Basic usage:

Get imperial representations of Date:

import { Chrono, Formats } from 'chrono-40k';

Chrono.classic.format(new Date());
// returns something like "0 227 025.M3"

Chrono.classic.format(new Date(), Formats.CLASSIC_SHORT_FORMAT);
// returns something like "025.M3"

Chrono.indomitus.format(new Date());
// returns something like "974.773 previo TCM.M3"

Chrono.indomitus.format(new Date(), Formats.INDOMITUS_ERA_SHORT_FORMAT);
// returns something like "974.773- TCM.M3"

Get Dates for imperial dates:

let date: Date = Chrono.classic.parse('005.M30').toDate();
// or
date = Chrono.classic.toTerranDate('005.M30');

Use imperial date objects:

const classicDate = Chrono.classic.parse(new Date());

console.log(classicDate.toString());
const date: Date = classicDate.toDate();

const indomitusDate = Chrono.indomitus.parse(classicDate);

Use short access to imperial dates:

let classicDate = Chrono.classic.parse(new Date());
// equals
classicDate = Chrono.parse(new Date());

console.log(Chrono.classic.format(new Date()));
// equals
console.log(Chrono.format(new Date()));

// etc.

Advanced usage

Convert from one imperial dating system the other:

const classicDate = Chrono.classic.parse('0 899 998.M41');
console.log(Chrono.indomitus.format(classicDate));
// outputs "1.101 previo TCM.M42"

Custom formatting

Chrono.classic automatically recognizes imperial dates in the formats

• c fff yyy.m (Formats.CLASSIC_DEFAULT_FORMAT)
  e. g. "0 550 899.M41" and
• yyy.m (Formats.CLASSIC_SHORT_FORMAT)
  e. g. "005.M30"

where c = check number, f = year fraction, y = year and m = millenium.

Chrono.indomitus automatically recognizes imperial dates into the formats

• y.f gg d.m (Formats.INDOMITUS_ERA_DEFAULT_FORMAT)
  e. g. "1.1 previo TCM.M41" and
• y.fg d.m (Formats.INDOMITUS_ERA_SHOR_FORMAT)
  e. g. "0.110+ TCM.M42"

where y = annual designator, f = chronosegments, g/gg = +/- or post/previo opening of the Cicatrix Maledictum, d = designator initials and m = millenium.

If needed, a custom format can be provided to any method that parses or formats and imperial date string:

Chrono.classic.parse('0123456  M7', 'cfffyyy m');
Chrono.classic.format(new Date(), 'yyy,m');

For more examples please take a look at the chrono.spec.ts

Remark

I intentionally diverge from the calculation of the year fraction (and the respective chronosegments in the "Era Indomitus" dating system) as I see a problem with the lore accurate calculation.

Problem

The first issue is that the fixed Makr constant does not take into account leap years. We need at least one "default" constant and one for leap years.

The second and more fundamental issue is that, even when not considering leap years, the calculation with the Makr constant just does not work.

E. g. calculate the year fractions for December 31, 2025 at 10 pm. December 31st is day number 365 of the year 2025 and 10pm is the 22th hour of that day so we calculate 365 * 24 + 22 = 8782. Then we multiply that with the Makr constant 8782 * 0.11407955 = 1001.84661 and round down the result to get the year fraction = 1001.

This is a problematic result as we just have 1000 year fractions in a year, so even when resolving this problem by just capping the result at 1000 we do not get a consistent way to calculate dates in both directions.

Solution

In my calculation I replace the Makr constant with two variations of the new Marco constant, one "default" and one for leap years.

marco_constant_default = 1 / ( ( 365 * 24 ) / 1000 )
marco_constant_leap_year = 1 / ( ( 366 * 24 ) / 1000 )

With theses adjustments the dating system does not work lore accurate anymore but it allows for a consistent conversion between gregorian and imperial dates.

Copyright

This software is completely unofficial and in no way endorsed by Games Workshop Ltd.