derived

Constants for readings Bitfount derives from data an EHR served.

A derived reading is computed from an Observation the EHR returned, not supplied by a site and not served as-is: an ETDRS letter count converted to logMAR, say. It is stamped with a Bitfount-minted code system so a criterion can address the canonical form without having to know which of the many representations a site's EHR happens to use.

Deliberately distinct from ENRICHMENT_CODE_SYSTEM (see bitfount.steps.types.enrichment), which means "a site's own export minted this code". Derived readings come from the EHR, so they carry EHR provenance and live in OBSERVATIONS_COLUMN; conflating the two systems would report EHR-sourced data as site-supplied.

---