# Introduction to Dimensions ## Overview Dimensions allow you to work with a collection of items without having to repeat calculations. > A Dimension might be: > > * **Widget Model** | Model A, Model B, and Model C > > or > > * **Sales Region** | North, East, West, and South Dimensions are extremely powerful, time-saving, and improve the quality of your Models. In the example screenshot below, the `Revenues by membership type` Variable has the `Membership Tier` Dimension applied. The `Membership Tier` has 3 children: `Basic`, `Premium`, `Platinum`.

The Variable has a single formula, `Gym members * Revenue per member`. The `[Auto]` suffixes in the formula imply that the Calculation is able to automatically reference the appropriate line of the referenced Variables, which both also have the `Membership Tier` Dimension applied. Using Dimensions, you can replace multiple sets of calculations with a single one, without worrying about copy/paste errors. ## Multiple Dimensions You can apply as many Dimensions as you like to a Variable. In the example screenshot below, the `Revenues by region and membership type` Variable has two Dimensions applied: `Membership Tier` and `Region`. Models calculates a value for each combination of the children of the two Dimensions, in this case 6 lines in total.

## Summarising Dimensions Models can create summaries of Dimensions easily - you don't need to worry about referencing the correct lines in a Calculation. In the example screenshot below, we want to show the total Revenues across the `North` and `South` regions from the `Revenues by region and membership type` Variable (see above [**Multiple Dimensions**](#multiple-dimensions) example). To do this we simply create a new Variable with the `Region` Dimension applied, and reference the `Revenues by region and membership type` Variable. Models does the rest for us automatically.