Enter a unit with an output factor

What causes this issue?

You want to define the output for an activity type and have entered the
respective output factor. However, to store an output in the data
bases, you need to enter a unit of output (such as piece).

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Enter the unit of output, or
Cancel the output factor again.

Error message extract from SAP system. Copyright SAP SE.