Seems like I can't get a patch attached to a bug report in the PDFTeX system, and Martin has closed the bug after fixing the first half. Here is a proposed patch to deal with the rest (note that 9.99998nd gets a wrong value, too, with the current code even though it adheres to Knuth's original description of the constraints). It also fixes Knuth's comment, and puts the nd ratio in shortest terms. The patch is based on LuaTeX, but it should be possible to apply it to pdfTeX. -- David Kastrup