Using UOM Operator
Appending the UOM operator to an attribute reference, tells the expression engine to convert the attribute value to the specified unit of measure. Otherwise, the attribute value will be returned without any further conversion.
Examples
Density
The result is the value of the attribute whose name contains Density string.
Density!Api
The result is the value, converted to Api, of the attribute whose name contains Density string.
"Density!Api"
The result is the value, converted to Api, of the attribute whose name is equal to Density.