Re: Round-off errors in metrics & fontinst/finst status...

["Berthold K.P. Horn" <bkph@ai.mit.edu>]

At 06:25 AM 97/12/18 +0000, Rebecca and Rowland wrote:

>And it can be less if the rounding is less than 0.5 - this 0.15mm is
>more-or-less worst-case.  The rms rounding error is something like 0.3, so
>the typical error with a repeated character will be nearer 0.05%, or 75
>microns in 150mm; typical error with random characters will be nearer 7.5
>microns.  I'm not inclined to fret over errors of less than 0.1mm across a
>page.

Ah, but even if noticable error only occurs in fixed width fonts and when
using the same character repetedtly, doesn't it bother you to spoil the
incredible accuracy that TeX has, just because of some unneeded sloppyness
in making fonts, or in making metric tables?

I might also mention that some DVI processors switch between relative
and absolute positioning.  This means accumulated errors can produce
a discontinuity at a transtion, not just at the end of the line.  This often
happens were a superscript appears.  In this case even a small error 
may be noticeable (0.15mm is 0.5pt)  (Although it should never be
as bad as it was in `The Hackers Dictionary' where several superscripts
where displaced by over an inch because DVIPS (at the service bureau) 
was looking at different TFM files form those used by the author's TeX 
when making the DVI file  :-)

Regards, Berthold.

Berthold K.P. Horn, MIT AI Laboratory
Cmabridge, MA USA	mailto:bkph@ai.mit.edu