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

Hans Hagen pragma at wxs.nl
Tue Apr 3 12:22:20 CEST 2007


David Kastrup wrote:
> 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.
>>     
>
> Well, but I would find a change rendering "1in"="72.27pt" attractive.
> I'll propose one shortly.  Anyway, those fractions carry _way_ more
> precision than TeX's general arithmetic anyway, and TeX's truncation
> (which this was all about in the first place) introduces more bias
> than this particular fraction does.  One could argue that 32163:2512
> will be a nicer fraction since it overshoots, and TeX forgets to round
> the final result, so we err on different sides.
>
> But I'd rather have the closest ratio and fix TeX's, excuse me
> (hopefully Knuth didn't hear), LuaTeX's arithmetic on units by letting
> it round properly.
>
>   
this is not going to happen soon, maybe a different 'rounding' some day;

while developing we need to be able to compare pdftex output with luatex 
output/processing and implementing a different rounding model is not 
convenient at this time

nobody bothered about that for 25 years so we're not in a great hurry 
there -)

Hans  

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