# [OS X TeX] bizarre preview difference for TeXshop and Adobe Acrobat

Thu Nov 19 07:27:45 EST 2009

On Nov 18, 2009, at 4:52 PM, Peter Dyballa wrote:

> Could you determine the relation of 72 DPI to your display's actual
> resolution?

The difference Ross is seeing is caused by his using the nifty feature
for adapting screen resolution to physical screen size (TeXshop should
add the same feature) --- one day this will be built in at the system
level an 100% will be 100% always.

The blank bit which initially led me down this path was caused by my
overlooking \topskip (my thanks to zappathustra on comp.text.tex for
explaining that) --- setting that to \textlineheight and then lowering
the rule by its width results in perfect positioning, except in
TeXShop and Preview.app (on my machine) when using Printer's Points
for measurements, so there's definitely a rounding error in Apple's
PDF object.

Changing the units to PostScript Points eliminates the previewing
error and TeXworks, since it uses Poppler doesn't have it w/ any unit.

William

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