[texhax] \magstep reduces text area

[David Carlisle]

On 19 July 2016 at 20:52, Rodolfo Medina <rodolfo.medina at gmail.com> wrote:
> David Carlisle <d.p.carlisle at gmail.com> writes:
>
>> plain tex sets hsize and vsize in "true in" units so they are not
>> affected by magnification, so if you magnify you have larger fonts
>> with the same physical area which appears expressed as same size
>> fonts, in a smaller physical area due to the way \mag works.
>>
>> David
>>
>>
>> On 19 July 2016 at 20:03, Rodolfo Medina <rodolfo.medina at gmail.com> wrote:
>>> I noticed that the use of \magstep, e.g.: \magnification=\magstep1 reduces
>>> considerably the text area.  Why?
>
>
> So you say that it would be only an eye effect?  But I'm sure the text area is
> really reduced, right margin is much larger...
>
> Thanks,
>
> Rodolfo
>

no I mean the measured size within tex will be less, but when scaled
back up it will be the same

plain does

\def\magnification{\afterassignment\m at g\count@}
\def\m at g{\mag\count@
  \hsize6.5truein\vsize8.9truein\dimen\footins8truein}

so hsize is 6.5in _after_ magnification is applied.


\showthe\hsize

\magnification=\magstep1

\showthe\hsize

\bye

produces

> 469.75499pt.
l.1 \showthe\hsize

?
> 391.46176pt.
l.5 \showthe\hsize

so hsize appears reduced but it will scale back to 6.5in.

David