# Defining Unit Variance by Dimension

## Overview

When you use [**Dimensions**](/dimensions/introduction-to-dimensions.md) in a [**Variable**](/variables/variable-basics.md), you may need to specify how each part of the Variable's [**Unit**](/units/introduction-to-units.md) varies.

> For example, in the screenshot below, our Variable has two (repeated) Dimensions replied: 1) Widget Supplier that a customer is moving **from**, and 2) Widget Supplier that a customer is moving **to**.
>
> In this case, the numerator (top) of the Unit refers to the "To" supplier, and the denominator (bottom) refers to the "From" supplier.

The user indicates how the unit parts should vary by using the toggle controls highlighted. This means that Models can correctly infer how to create the Units for [**Assumptions** ](/assumptions/introduction-to-assumptions.md)and how to correctly reference Variables in [**Calculations**](/calculations/introduction-to-calculations.md).

<figure><img src="/files/kvryG6lWPxC0bDYuYFWX" alt="Screenshot showing the Unit step of the Variable wizard, with two &#x22;Widget Supplier&#x22; dimensions applied"><figcaption><p>Selecting Unit Variance with Dimensions</p></figcaption></figure>


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