Units of measure — Changing a column's unit

Move a column from kilograms to grams and the stored values move with it — multiplied through exactly, once, inside the same save, with the confirmation telling you how many changed. It is the only configuration change in RowFold that rewrites records, and it does so because the alternative is worse: leaving the numbers alone would keep the same digits under a new label and silently restate every one of them by a factor of a thousand. Changing to a unit in a different class is refused, for the reason in section 04 — there is no exact factor to apply. An empty column can be set to anything, because there is nothing to restate.