# Referencing Dimensions ## Auto Relationships When you create a reference to a Variable that has [**Dimensions**](/dimensions/introduction-to-dimensions.md), Models needs to know which items within that Variable to reference when performing Calculations. Most of the time, Models can automatically work out which items to reference. For instance, in the example below, `Revenues by region and membership type` has the [**Calculation**](/calculations/introduction-to-calculations.md) `Gym members [Auto] * Revenue per member [Auto]`. The `[Auto]` suffix to the Variable references indicates that Models will automatically deduce the correct relationships, based on Dimensions. `Revenues by region and membership type` and `Gym members` both have two Dimensions: `Region` and `Membership Tier` - they vary both regionally and by gym package. `Revenue per member` only has one Dimension, `Membership Tier`, as the price of the gym does not vary by region. For each item of `Revenues by region and membership type`, Models will take the matching line from each of the reference Variables.

Example: Automatic Dimensions references. NOTE: Displayed values are rounded and will not produce calculated outputs shown

## Custom relationships We can configure the way that Dimensions are referenced. For example, let's say we want to create a new Variable called `Revenue if everyone is Platinum`. We use the same formula as in the example above (`Gym members * Revenue per member`), but this time we want the `Revenue per member` reference to only use the `Platinum` value. To do this, we open the Calculation Part wizard for the `Revenue per member` Variable Reference, and navigate to the **Reference type** step, as shown below:

Screenshots showing how to create a custom relationships to a Variable using the Calculation Part editor wizard — Setting a Custom Dimension relationship

In the item match dropdown, we select a **Custom** match **(1)**. A new step is displayed which allows us to customise the match for the `Membership Tier` Dimension. Here, we can specify that it should always link to the `Platinum` item **(2)**, rather than varying based on the source Variable's Dimension. This results in the desired calculation, as shown below:

Example: Custom Dimensions references. NOTE: Displayed values are rounded and will not produce calculated outputs shown

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