This code system http://hl7.org/fhir/substance-amount-type defines the following codes:

Code Display
Average Average
Approximately Approximately
LessThan Less Than
MoreThan More Than
<status value="draft"/> <experimental value="false"/> <date value="2021-01-05T10:01:24+11:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="The type of a numeric quantity measurement."/> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/substance-amount-type"/> <content value="complete"/> <concept> <code value="Average"/> <display value="Average"/> </concept> <concept> <code value="Approximately"/> <display value="Approximately"/> </concept> <concept> <code value="LessThan"/> <display value="Less Than"/> </concept> <concept> <code value="MoreThan"/> <display value="More Than"/> </concept> </CodeSystem>