This is the CodeSystem that contains all the codes in BRUnidadeMedida (https://terminologia.saude.gov.br/fhir/CodeSystem/BRUnidadeMedida) and BRUnidadeMedida (https://terminologia.saude.gov.br/fhir/CodeSystem/BRUnidadeMedida). E.g. what you have to deal with if you get resources containing codes in either of them