The rulers were handed out at CERL events, and are available upon request as long as stocks last.

Paul Needham explains its use:
'What incunabulists typically see are not uncut sheets of paper, but rather bound volumes, with varying degrees of trimming. My recommendation, therefore, is to think in terms of very large copies of folio incunables printed using each of the 8 distinct paper sizes. What this ruler provides are these “nearly-maximum” heights and widths. Please note: (1) Most copies will be smaller in both dimensions than the measurements provided, due to shaving of edges by binders. (2) There are only a few Super-Median incunables. (3) Half-Median size is found in a dozen or so Franciscus Renner editions of the 1470s, always or almost always used together with half-sheets of Median paper.'

A diagram to show which paper sizes, in which formats, are actually represented by at least one incunable edition.