From Pugin's Specimens of Gothic architecture; selected from various antient edifices in England (Volume II) (1823)
Sp Coll RQ 1603

"The form of vaulting, here displayed, has been frequently termed the fan-groin, from the manner in which its tracery seems to expand ... The stones of which this vault is formed are marked at the joints; the sweep of the diagonal rib is drawn in dotted lines upon the plan; with several other particulars necessary to the full development of the construction.
A. Perpendicular section of the structure.  B. Horizontal delineation.  . Plan of the entrance on a small scale.  The opening on the left leads, by a spacious flight of steps, from this gate to the great hall"

(pages [4]-5)