http://hl7.org/fhir/StructureDefinition/Quantity|5.0.0

Quantity Type: A measured amount (or an amount that can potentially be measured). Note that measured amounts include amounts that are not precisely quantified, including amounts involving arbitrary units and floating currencies.
NameFlagsCardTypeDescription & Constraints
Quantity
0..*A measured or measurable amount
 
value
Σ
0..1decimalNumerical value (with implicit precision)
 
comparator
?!Σ
0..1code< | <= | >= | > | ad - how to understand the value QuantityComparator (required)
 
unit
Σ
0..1stringUnit representation
 
system
Σ
0..1uriSystem that defines coded unit form
 
code
Σ
0..1codeCoded form of the unit