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

[David Kastrup]

Taco Hoekwater <taco at elvenkind.com> writes:

> David Kastrup wrote:
>> But I consider it more likely that nc should be changed to 1370:107
>
> And also, I applied this change to luatex.web (and fixed the
> documentation sting back). TeX's conversions are approximations
> anyway, I see little point in changing the conversion arithmetic.

Unfortunately, Knuth is a practical joker.  The old documentation
string, while sounding reassuring, is actually also wrong.

With the code he has written there, the requirement is that the _sum_
of num and denum does not exceed 32768.  Which happens to be the case
for his ratios, but not for _either_ of the new ones.

Check the following:

This is luaTeX, Version 3.141592-snapshot-2007040210 (Web2C 7.5.6)
**\relax

*\dimen0=9.9998nd

*\showthe\dimen0
> 7.44438pt.
<*> \showthe\dimen0
                   
? 

*\dimen0=10nd

*\showthe\dimen0
> 10.66977pt.
<*> \showthe\dimen0
                   
? 

*

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
closest usable ratio which is 11183:10481.

So it looks like neither the new cicero nor the new didot have a
chance to be represented exactly.  Too bad.

I am still being sidetracked from what I really wanted to look at.

Does anybody actually _use_ those new dimensions?

-- 
David Kastrup