# Reference variables

A reference variable holds a unique reference for each record, such as a Household URN (unique reference number) or a Supporter ID. Each table has one. The data picker shows reference variables with a barcode icon.

Filter by a reference variable to include or exclude specific records, such as a seed list or supporters who've asked not to be contacted.

## Filter by a reference variable

You can type the references in, or use a file of them.

To filter by a reference variable:

1. Choose an option from the dropdown:

   - **Is**: Includes the records with these references
   - **Is not**: Excludes the records with these references
2. On the **Values** tab, type or paste up to 100 references, one on each line or separated by commas. For more references, [use a file](<#use-a-file-of-references>).
3. Select **Apply**.

> [!TIP]
>
> For more than a handful of references, use a file. It keeps your filter manageable, and it's easier to update the list later.

## Use a file of references

Use the **Upload File** or **Existing File** tab, as described in [Use a file of values](<https://help.apteco.com/en/orbit/data/variables/#use-a-file-of-values>).

For a reference variable, the file must:

- Be a `.TXT` or `.URN` file
- Have one reference on each line. Separators are ignored.

A file of references you've saved is a URN file, and you can also use it from the **Files** tab of the data picker. See [Audiences and files](<https://help.apteco.com/en/orbit/data/audiences-and-files/#files>).

On a dashboard, you can choose whether Orbit keeps an uploaded file permanently or only while you need it. See [URN files in dashboard filters](<https://help.apteco.com/en/orbit/dashboards/filtering/temporary-urn-files-in-dashboard-filters/index.md>).