Drawings change. A revision records what changed, when and by whom; clouds and triangles show where on the sheet; a transmittal records who was sent which revision. Together they let anyone prove which version they built from.
A drawing is never finished until the project is. Each change produces a new revision of the sheet, and on a busy project dozens of sheets change every week. Revisions and transmittals are the bookkeeping that lets anyone answer two questions with evidence: what changed, and who knew.
Sheet 4 of the Benton Street Bridge was made in January 1948. Under its title block someone has written "Rev. E.J.W. 11-15-48": a revision made on 15 November 1948, initialled. There is no description, no cloud and no revision code. Almost eighty years later, that's still enough to know the sheet changed, but not what changed. A modern revision table adds exactly the missing pieces.
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