# How do you effectively debug overfull \hbox warnings?

I still haven't found out how to effectively solve Overfull \hbox (0.80913pt too wide) has occurred while \output is active warnings.

For instance, this piece of latex generates such a warning and I am stumped why:

\newcommand\Header{%
\noindent\makebox[\textwidth][l]{
\parbox{0.5\textwidth}{\contactinfo}
\parbox{0.5\textwidth}{%
\hfill\includegraphics[height=25pt]{logo}}}\par\vskip1ex%
\par\ColTopRule\par}


\contactinfo is defined as follows:

\newcommand\contactinfo{\fontsize{8pt}{8}\selectfont\headerfnt Streetname 12324 \\ PostalCode City \\ +31655555555555}


Error:

*geometry detected driver: pdftex*
<logo.eps>
Overfull \hbox (0.80913pt too wide) has occurred while \output is active
[]
[1] <logo.eps>
Overfull \hbox (0.80913pt too wide) has occurred while \output is active
[]
[2] <logo.eps>
Overfull \hbox (0.80913pt too wide) has occurred while \output is active
[]
[3] <logo.eps>
Overfull \hbox (0.80913pt too wide) has occurred while \output is active
[]


Expected output is:

Streetname 12324                                       here comes
PostalCode City                                          the logo
+31655555555555                                     right aligned
-----------------------------------------------------------------


I mean, both boxes have a length of 0.5\textwidth, the text is obviously smaller than this, as is the logo. How come it still generates such a warning? And how can I found out why?

-
You need to escape spaces with %. E.g. \noindent\makebox[\textwidth][l]{% –  Marco Daniel Apr 13 '12 at 11:50
did that: \newcommand\Header{% \noindent\makebox[\textwidth][l]{ \parbox{0.5\textwidth}{\contactinfo} \parbox{0.5\textwidth}{% \hfill\includegraphics[height=25pt]{logo}}}\par\vskip1ex% \par\ColTopRule\par} error remains –  grrrbytes Apr 13 '12 at 11:54
hard to see in the comment formatting but you still have a space before each of the \parbox commands in that comment –  David Carlisle Apr 13 '12 at 11:58
weird, I removed all spaces. To no avail –  grrrbytes Apr 13 '12 at 12:01
\makebox[\textwidth]{...} doesn't care if you put something larger than \textwidth in it. So I doubt that the problem is from the content. I guess that you either have a additional space at the place where you use your \Header command or a non-zero \parfillskip value. Make a complete example. –  Ulrike Fischer Apr 13 '12 at 12:37

\showboxdepth=\maxdimen

\showboxdepth=5