# Linking Drivers to Variables

This article explains how to **link drivers to variables** in Model Reef.

You will learn:

* The different ways drivers can feed variables.
* How to configure links in presets and formulas.
* How changes in drivers propagate to financial outputs.

Drivers only affect financial statements when they are linked to variables.

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### Linking via presets

Many variable presets allow you to link drivers directly, for example:

* Selecting a volume driver to determine units sold.
* Selecting a price driver to determine revenue per unit.
* Selecting an inflation driver to escalate costs over time.

In these cases you choose the driver from a picker within the preset configuration. The preset then reads the driver values each period.
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### Linking via formulas

You can also link drivers using explicit formulas, for example:

* `Revenue variable = Units driver × Price driver`
* `Cost variable = Base cost driver × Modifier driver`

Here you enter the relationship in the **Formula modal**, and the variable's time series is entirely determined by the formula.
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### Linking via Data Library entries

Sometimes a Data Library entry encapsulates both:

* An imported series.
* Driver based forecasts.

Variables that reference the entry implicitly link to whatever driver logic is defined there. Editing the entry updates all linked variables at once.
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### Propagation of driver changes

When you change a driver that is linked to variables:

* The driver time series updates.
* All variables that use that driver recalculate.
* P\&L, Balance Sheet, Cashflow and Cash Waterfall update in the active scenario.
* Dashboards, charts and valuation outputs update automatically.

This is the core advantage of driver based modelling: a single assumption change can update many parts of the model coherently.
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### Traceability

To understand how a variable is driven:

* Open the Variable Editor.
* Review preset and formula sections for driver references.
* Use notes to document key driver relationships.

This makes it easier for reviewers to see which assumptions are central and where they live.
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***

## Related articles

* [Overriding Variables](/syntax/scenario-syntax/overriding-variables.md)
* [Selecting Drivers in Sidebar](/syntax/formula-syntax/selecting-drivers-in-sidebar.md)
* [COGS Variables: what is, rules, what it affects](/help/drivers-variables-and-timing/cogs-variables.md)
* [Build a Stress Test / Downside Case](/how-tos/scenarios-and-planning/build-a-stress-test-downside-case.md)


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