Ancient Dwarven Calendar

The Ancient Dwarven Calendar was previously the standard time keeping method for Dwarves back in the day when they prospered within Dwarven Fortress. In the present time, most Dwarves have merged with the rest of modern society and use the Dwarven Calendar.

Their ancient calendar is centered around the work shift. It revolves around a base unit of time measurement and each greater duration of time increases in regular intervals from there.

Seasons

Ancient Dwarfs, who would spend most of their lives in their mountain fortress holds, had no need to keep track of seasons, since they lived mostly underground. They recognized two major seasons: Lean and Prosper. During Lean, they would hunker down, and farm cave mushrooms and subterranean livestock. During Prosper, they would venture outside, let their livestock graze on the slopes, forage, and trade for exotic foods.

Months

The concept of a "month" was also largely irrelevant to the Ancient Dwarven lifestyle. In other calendar systems, months are based on lunar cycles which does not interest subterranean people.

The concepts of day and night are also irrelevant to the Dwarven peoples. Their lives largely centered around work productivity and they did have a 24 hour circadian circle like most surfaces dwellers do.

Timekeeping

Ancient Dwarves measured time using this system based on a work shift.

Lantern: The basic unit of time measurement is a Lantern - the approximate amount of time a small oil hand lantern will burn without re-filling (approximately an hour).

Shift: 10 Lanterns is a Shift. This is how much time you are expected to put in at your job. Everyone gets a Work Shift, and then an Rest Shift, which make up a Rotation. Shifts are staggered so that there's always Dwarves working as others rest, and their mines and workshops never close.

Stint: 10 Rotations is a Stint which is close to a week of time, and a basic concept used by merchants and workers. For example, you might get hired for a fixed number of Stints, or you may agree to deliver merchandise in a number of Stints specified in contract.

Span: 10 Stints is a Span (about 3 months) which is also about the amount of time it takes a smith to produce a good quality, fitted plate armor set.

Term: 10 Spans is a Term (about 3 years) which is a standard way of measuring length of apprenticeship. An apprentice is expected to work anywhere between one or a few dozen Terms under a master craftsman before they can enter guilds or work independently. The lengths of apprenticeship vary based on the profession. Manual laborers, for example only need to put in one Term, whereas Smiths or Engineers must spend many.

Age: 100 Terms (about 300 years) is an Age. This also an approximate lifespan for an average Dwarf.

Reference

Unit	Length	Time Reference	Description
Lantern		about an hour	time it takes to burn a small lantern
Shift	10 Lanterns	about 10 hours	Typical works shift
Rotation	2 Shifts	about 20 hours	work shift, followed by a rest shift
Stint	10 Rotations	little over a week	short term contract, or work agreement
Span	10 Stints	about 3 months	time it takes to craft a plate armor set
Term	10 Spans	about 3 years	typical length of an apprenticeship
Age	100 Terms	about 300 years	average Dwarf lifespan