http://hl7.org/fhir/StructureDefinition/observation-precondition|5.2.0

Other preceding or concurrent observations that must be known to understand the context and significance of the observation. For example, an fiO2 measure taken alongside of a SpO2 measurement. See the FHIR specification [Observation notes](http://hl7.org/fhir/observation.html#notes) section for additional guidance.