These helpers construct durations of the specified precision. Durations represent units of time.

Durations are separated into two categories:

**Calendrical**

year

quarter

month

**Chronological**

week

day

hour

minute

second

millisecond

microsecond

nanosecond

Calendrical durations are generally used when manipulating calendar types, like year-month-day. Chronological durations are generally used when working with time points, like sys-time or naive-time.

## Usage

```
duration_years(n = integer())
duration_quarters(n = integer())
duration_months(n = integer())
duration_weeks(n = integer())
duration_days(n = integer())
duration_hours(n = integer())
duration_minutes(n = integer())
duration_seconds(n = integer())
duration_milliseconds(n = integer())
duration_microseconds(n = integer())
duration_nanoseconds(n = integer())
```

## Internal Representation

Durations are internally represented as an integer number of "ticks" along with a ratio describing how it converts to a number of seconds. The following duration ratios are used in clock:

`1 year == 31556952 seconds`

`1 quarter == 7889238 seconds`

`1 month == 2629746 seconds`

`1 week == 604800 seconds`

`1 day == 86400 seconds`

`1 hour == 3600 seconds`

`1 minute == 60 seconds`

`1 second == 1 second`

`1 millisecond == 1 / 1000 seconds`

`1 microsecond == 1 / 1000000 seconds`

`1 nanosecond == 1 / 1000000000 seconds`

A duration of 1 year is defined to correspond to the average length of a proleptic Gregorian year, i.e. 365.2425 days.

A duration of 1 month is defined as exactly 1/12 of a year.

A duration of 1 quarter is defined as exactly 1/4 of a year.

A duration of 1 week is defined as exactly 7 days.

These conversions come into play when doing operations like adding or
flooring durations. Generally, you add two calendrical durations together
to get a new calendrical duration, rather than adding a calendrical and
a chronological duration together. The one exception is `duration_cast()`

,
which can cast durations to any other precision, with a potential loss of
information.