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.

The Schoenberg Institute for Manuscript Studies has created a tool that will be useful to manuscript scholars, art historians, incunabulists, and all those interested in the categories and formats of fifteenth century paper, and the impact they had on the sizes of books and works of art as we see them today.

The tool is called the Needham Calculator because it is dependent upon Paul Needham’s classification of categories of fifteenth-century paper.

An explanation of the calculator and how it was created is available here.