A unit can be linked to a unit category. It is of course possible that the unit category changes over time.
Please follow the steps below to change the unit category.

From the unit page:

1. Select the line(s) for which the Unit Category has to be changed. The line(s) should have shaded yellow

2. Click the blue button Change Unit category

3. Select the desired Unit Category

4. Confirm your choice by clicking on the blue Save button.