Distinguish between unitless attributes and attributes whose units have not been assigned
It is difficult to tell on which attributes and attribute templates PI administrators forgot to add unit labelling when the default default UOM and the UOM to indicate unitlessness are the same: <None>.
Instead, the default default UOM and the UOM to be used when the unit is unknown should both be <Unassigned>, and <None> should be reserved for unitless attributes and attribute templates.
Kenneth Barber commented
The "default default UOM" is not a mistake. "Default UOM" is a property of attributes and attribute templates. The default "Default UOM" is always <None>.