UO has been used in various OBO ontologies, including the Ontology for Biomedical Investigations (OBI), The Statistical Methods Ontology (STATO), and HUGO-PSI Mass spectrometry ontology (MS).
The HUPO-PSI mass spectrometry controlled vocabulary (PSI-MS) uses UO terms as the units of the quantitative terms it defines for the mzML and related PSI data standards.