From 1792 to 1799, astronomers Jean-Baptiste-Joseph Delambre and Pierre Mechain surveyed the meridian arc from Dunkirk to Barcelona by triangulation to define the metre as one ten-millionth of the distance from pole to equator. The expedition stretched across the chaos of the Revolution, arrests as suspected spies, war, and illness, taking seven years for what was planned as a short mission.
Mechain discovered a discrepancy between two sets of latitude readings he took at Barcelona and, unable to reconcile them, hid the inconsistency rather than reveal it, falling into years of secrecy and depression over the flaw. The concealed error meant the official metre was very slightly off from its intended natural definition, a mistake buried in the archives and uncovered only later by the author's reconstruction.
Mechain treated measurement discrepancy as shameful proof of personal failure to be hidden, whereas the later statistical insight was that systematic variation in repeated measurements carries real information about the quantity and its uncertainty. The development of error theory grew partly from wrestling with exactly the kind of irreducible discrepancy that destroyed Mechain.
The metre was deliberately defined from the size of the Earth so that its authority would rest on nature rather than on any king or nation, making it a standard anyone could in principle reproduce and no sovereign could own. In practice the physical platinum bar, not the Earth measurement, became the operative standard, showing that an abstract natural definition still collapses into a chosen artifact.