# Available periods

When a projection is created, Time Series assigns it a `start_date`

and an `end_date`

, the interval between these two values is called a **period**. Therefore, you can consider it as the "life span" of your projection.

A period is usually composed of two parts, a **number** followed by a **type**; the only exception is regarding the global period.

Here is a list of valid periods: `*`

, `1 day`

, `2 hours`

, `3 months`

, `1 year`

, `12 hours`

.

## Types of periods

Laravel Time Series gives you access to these different types of periods:

`*`

`minute`

`hour`

`day`

`week`

`month`

`year`

Note that you should pluralize the period's type if the duration is greater than `1`

.

## The global period

##### info

A projection with a global period doesn't have a `start_date`

or `end_date`

.

In case you want to build a projection with an unlimited lifetime, add the `*`

period to your projection.

A projection with a global period will be unique (regarding the `*`

period) and continuously updated by the bound projectable models.

## What happens when you add several periods to a projection?

You can consider that a projection with X periods is actually X separate projections. Separate rows in the `time_series_projectable`

table will be created for each period added to a projection.

For example, if you define a projection with three periods, each time a bound model fires an event, three rows will be updated in the database, one for each period.

## How a projection's start date is defined?

A projection's `start_date`

is defined regarding its period and the current date. Each time a new one is created, its `start_date`

will equal **the current date rounded to the floor by the given period**.

For example, let's say the current date is `2022-01-07 11:04:25`

:

- Given a
`1 hour`

period, the start date equals`2022-01-07 11:00:00`

. - Given a
`2 hours`

period, the start date equals`2022-01-07 10:00:00`

. - Given a
`1 day`

period, the start date equals`2022-01-07 00:00:00`

. - Given a
`2 days`

period, the start date equals`2022-01-06 00:00:00`

. - Given a
`1 week`

period, the start date equals`2022-01-03 00:00:00`

.