Measurement
Verification
Verification is an independent third party checking that a project did what it reported, against a published methodology. It is the step that makes a carbon claim worth anything to a buyer, and the step most often reduced to a document review conducted at a distance.
A verifier checks what was recorded, so records collected continuously as the work happens are what make verification straightforward.
That is the practical reason sensors go in from day one, before the first buyer asks.