Many key ocean variables are defined by consensus without a clear linkage to the international system of units (SI). As the amount of data from diverse sources and platforms increases, measurement bias and discrepancies in signal-to-noise-ratio emerge, complicating the detection and quantification of Global Change effects. Thus, metrology (the science of measurements) becomes increasingly important. This session invites studies that evaluate the impact of instrument calibration, metrological traceability, and the use of reference materials on marine biogeochemical measurements. Focus areas include the seawater carbonate system, dissolved inorganic nutrients, dissolved oxygen, and carbon and oxygen isotopes. This session will discuss how accurate calibration enhances data reliability, improves reproducibility, and drives scientific advancements in marine biogeochemistry. The session will promote dialogue between metrologists, oceanographers and manufacturers to shape a future where data legacy is guaranteed.