Units of measure — Every way a value arrives (2)

• Spreadsheet import: The likeliest place for a genuinely mixed column, because that is how the source system printed it. A cell whose unit cannot be read keeps its raw text for the import's own validation to report — an unattended run over 5,000 rows must not abort on row 4,881. Why this is listed rather than assumed: a converter wired into only some write paths is worse than none. The same text would convert when typed and store a literal when pasted one row down — two cells, the same input, a thousandfold apart, with no error either time. All of these go through one converter.