A historic broadside paper size in the British imperial system, typically measuring 15.5 by 19.25 inches. It was widely used for writing paper and ledgers. When folded into smaller formats, it yields standard book sizes like post octavo.
Heard on the job
The ledger needs to be bound in large post, so pull the heavier stock from the back rack.
Insider tip
The name comes from an early watermark of a post horn used by papermakers.