Error converting the creation unit of measure

What causes this issue?

The specified unit of entry does not correspond to the base unit of
measure. The system cannot convert it to the base unit of measure as
the conversions factors have not been maintained in the material master
record nor has the unit of measure been defined in the Table containing
the unit of measurements.

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?

Either enter another unit of measure or enter the conversion factor in
the material master record.

Error message extract from SAP system. Copyright SAP SE.