traceability
/ tray-suh-BIL-ih-tee /
Every banknote can be tracked back through a chain of records to the central bank that printed it, which is what makes a stranger willing to accept it. Traceability is that unbroken chain of trust for a measurement: every value can be linked, step by step, back to an agreed reference, so a result measured in one lab means the same thing as one measured anywhere else.
Metrological traceability is the property of a measurement result whereby it can be related to a stated reference — usually a national or international standard — through an unbroken chain of comparisons, each with a stated uncertainty. Your reading is traceable if you can show the line of calibrations that ties your balance, your standards and your method back to the kilogram, the mole or another defined unit.
It matters because without traceability a number is just a private opinion: it cannot be compared with a number from a different lab, country or year. The honest caveat is that each link in the chain adds its own uncertainty, so traceability does not make a result exact — it makes it comparable and honestly bounded, with the uncertainty growing as the chain lengthens.
A lab weighing balance is calibrated with reference weights that were themselves calibrated against a national mass standard, which is tied to the international definition of the kilogram — so a mass read on that balance is traceable all the way to the SI unit.
An unbroken calibration chain linking a result back to an SI unit.
Metrological traceability (linking a value to a reference standard) is a different idea from sample traceability or chain of custody, which is the paper trail tracking which physical sample was handled when and by whom.