Level "Psuedo Units" defined from a log ratio. This includes any number of units like deciBels where the unit is derived as a log ratio of two other units. The logarithm distinguishes these from other dimensionless ratios. Dimensionless Ratio UCUM http://unitsofmeasure.org/ucum.html#para-46 "Psuedo Units" defined from a log ratio ODM2 Units Type Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of the Unit or the more general quantity that the Unit represents.