# Unit and Calculations

The **Unit** and **Calculation** of a Variable (if required), each have a dedicated step in the Variable wizard.

<figure><img src="/files/cPwz6PjZV21NWWLHCsHZ" alt="Two screenshots. The left hand side screenshot shows the Units step of the Variables dialog. The right hand side shows the Calculation step of the Variables dialog."><figcaption><p>Unit and Calculation steps of the Variable dialog</p></figcaption></figure>

{% hint style="info" %}
If this is your first time defining a Unit, we recommend reading the [**Introduction to Units**](/units/introduction-to-units.md) first
{% endhint %}

## Infer/Specify unit

A Calculation Variable can derive its Unit automatically, based on the Variables that it references.

> For instance, a Variable called `Revenues` has a Calculation `= Widgets Sold * Price`, where `Widgets Sold` has a Unit of `Widget`, and `Price` has a Unit of `US Dollars / Widget`. In this case, the Revenues Variable can infer that its Unit is `US Dollars`

Sometimes you will want to specify the Variable's Unit explicitly. In this case, select the **Specify Unit** option, and the Unit-editing page of the dialog will be shown.

> For instance, a Variable called `Customers` has a Calculation = `Customers [-1] + New customers`. This Variable references the previous period of itself, so cannot infer its Unit automatically. In this case, you will need to specify the Unit explicitly.

Read more about Units [**here**](/units/introduction-to-units.md).

{% hint style="info" %}
You will only see the Infer/Specify unit step if you have selected the **Calculation** Variable type. **Assumption** and **Aggregation** Variables must specify Units explicitly.
{% endhint %}


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