[NTG-pdftex] [Dev-luatex] What is the unit "nc" supposed to be?

David Kastrup dak at gnu.org
Tue Apr 3 14:52:51 CEST 2007

Taco Hoekwater <taco at elvenkind.com> writes:

> David Kastrup wrote:
>> So I recommend that you change the ratio of nd either to 1370:1284
>> (which reinstates the 12nd=1nc relation), or better change it to the
> I picked that choice for luatex. People would be awfully confused if
> 12pt!=12pc,

I'd be confused it it were...

> so I suspect the same is true for nds and ncs (assuming anyone
> actually uses these units, which is doubtful at this stage).

I'd probably prefer the more exact value 11183:10481.  Both nc and nd
don't exist in the wild, they are only abstract ratios inside of TeX.
If people specify a value in the smaller unit nc, they presumably want
to have it heeded as well as possible.

But since those values differ only in the seventh place, the
five-digit precision of TeX's "scaled" values will probably make that
difference irrelevant for most applications.

Your choice makes x nd equivalent to 12*x nc, where x is a "scaled"
15.16 fixed point number from TeX.

I have the sneaking suspicion that Knuth might have known about these
units and decided not to put them into TeX since they did not have
convenient exact ratios like the others.

David Kastrup

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