UCUM (Unified Code for Units of Measure) provides a system of units that is unambiguous and machine-processable, used in myHealth@MyHands to standardise the representation of quantitative laboratory results, vital signs measurements, and dosage values across all Member State data contributions. UCUM is mandatory for semantic interoperability of the Laboratory Results Dataset and ePrescription Dataset within the myHealth Master Data layer. Without UCUM, unit-of-measure fields in cross-border clinical data exchanges cannot be reliably compared or aggregated.