Using Drivers in Formulas

This article explains how to use drivers in formulas in Model Reef.

You will learn:

• How to reference drivers in the Formula modal.

• How drivers combine with variables and other series.

• Patterns for building driver based formulas safely.

Drivers are read-only time series that you plug into variable formulas and custom chart formulas.

1

Referencing drivers in the Formula modal

When you open the Formula modal for a variable or custom series:

• A sidebar shows available drivers grouped by type.

• You can click a driver to insert a reference into the formula.

• You can also start typing the driver name and use autocomplete.

The inserted reference represents the entire time series, not a single cell.

2

Arithmetic-only formula engine

The formula engine supports arithmetic only:

• Addition +

• Subtraction -

• Multiplication *

• Division /

• Parentheses ( )

No IF statements, logical operators or cell-based references are allowed. Formulas operate on entire time series at once.

3

Common driver formula patterns

Examples of patterns using drivers:

• Price and volume

  • Revenue = Units driver × Price driver

• Inflation or growth

  • Cost = Base cost × (1 + Inflation driver)

• FX adjustment

  • Local amount = Foreign amount × FX driver

• Scenario multiplier

  • Scenario result = Base result × Scenario modifier driver

Because everything is vectorised, the formula is applied across all periods of the model horizon.

4

Combining drivers with variables

You can combine drivers with variables, for example:

• New variable = Existing variable × Modifier driver

• Margin % = (Revenue variable - COGS variable) ÷ Revenue variable

The engine takes care of aligning time indexes so that operations occur period by period.

5

Validation and previews

The Formula modal provides:

• Syntax validation to check the formula is structurally correct.

• A preview of the resulting series, so you can see if the pattern looks right.

If a driver reference is removed or renamed, you will see an error until the formula is updated.

Related articles

• Linking Drivers to Variables

• Overriding Drivers

• Economic Drivers

• Build a Staffing Cost Model