description: 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. Use Observation.intpretationContext after R5. package_name: hl7.fhir.uv.extensions.r3 derivation: constraint name: ObsPrecondition type: Extension elements: extension: {index: 0} url: pattern: {type: Uri, value: 'http://hl7.org/fhir/StructureDefinition/observation-precondition'} index: 1 value: choices: [valueReference] index: 3 valueReference: type: Reference choiceOf: value refers: ['http://hl7.org/fhir/StructureDefinition/Observation'] index: 4 package_version: 5.3.0-ballot-tc1 extensions: {} class: extension kind: complex-type url: http://hl7.org/fhir/StructureDefinition/observation-precondition base: http://hl7.org/fhir/StructureDefinition/Extension version: 5.3.0-ballot-tc1 required: [valueReference, value]