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.

From the Schoenberg Institute page: 'Paper moulds were made in standard categories, but not in exact standard measures. Below we give the maximum size for each category, as established by Needham for half sheets (folio format), and we have extrapolated these sizes for the various different formats in which these papers are found. The formats result from the sheet being folded successively in half in various orientations: