A while ago I found out that there are two hardly known units available at least in pdftex: nd and nc for a Didot point of 0.375 mm as exactly as TeX can represent it in sp and the corresponding cicero of 12 points. From Q319652:

So 1238/1157 pt/dd or pc/cc is indeed exact and there are actually two units for the “metric Didot point” of 375 µm and its cicero: nd and nc:

  • 1nd = ⌊685/642 pt⌋ = 69925sp ≈ 0.375mm
  • 1nc = ⌊1370/107 pt⌋ = 839105sp ≈ 4.5mm

However, these units are not mentioned in Knuth's TeX Book and tex.web §458. When have they been added and where are they available?


The pdftex manual texdoc pdftex section 7 says

Two new units of measure were introduced in pdfTEX 1.30.0:

With texlive engines at least, nd is recognised in etex, pdftex, luatex, but not tex, xetex, ptex, uptex, euptex

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