Primary data

Data measured at its source — your meter, your supplier's actual production — as opposed to an industry average.

Primary data comes from the process being described. Secondary data is a stand-in: an average, a proxy, a database entry for something similar.

The difference is not academic. A footprint built on averages cannot detect that you changed supplier, switched fuel, or improved a process, because none of those change the average. It is a number that cannot be managed.

Most inventories are a mixture, and there is nothing wrong with that. What matters is that the mixture is visible — that a reader can see which parts of a figure are measured and which are assumed, rather than being handed one number with a uniform appearance of precision.

Scope 3 All other indirect emissions across the value chain — purchased goods, transport, use of sold products, end of life.
Precursor An input that already carries embedded emissions of its own — the steel in a bolt, the clinker in cement.
Provenance tier A label recording how a figure was obtained — measured, calculated, estimated or declared — kept separate from the figure itself.