# Overfull hbox on a tiny equation?

My microscopic equation is 2.8 points too wide for some reason, which is quite a lot. I am reluctant to ignore the warning because if I get more of them I'll start missing important things.

Code is:

Applying Snell's law (Equation \eqref{eq:snell}) twice gives us:
\begin{align}
\theta_2 &= arcsin \left( \frac{n_{vacuum}}{n_{mylar}} sin(\theta_1) \right) \\
\theta_1 &= arcsin \left( \frac{n_{mylar}}{n_{vacuum}} sin(\theta_0) \right)
\end{align}
which simplifies to
$$\theta_2 = \theta_0$$
We saw earlier that there was a critical angle [blah blah more text...]


And the warning is:

Overfull \hbox (2.80157pt too wide) (page 6)


on line 226, which is the line containing the tiny \theta_2 = \theta_0.

I'm probably missing something relatively obvious but I just can't see it. Any idea ?

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## migrated from stackoverflow.comJun 8 '11 at 13:36

This question came from our site for professional and enthusiast programmers.

Your code snippet works OK for me (no overfull warning). Can you reduce your actual code to a minimal, compilable version illustrating the problem? –  Gonzalo Medina Jun 8 '11 at 13:42
On an unrelated note, I recommend using \sin and \arcsin. –  fudo Jun 8 '11 at 13:50
@Niriel It's quite strange and I suspect that it has nothing to do with that equation in particular. However it is necessary to know if you have tried some customization of the equation numbers. Please add the document's preamble. –  egreg Jun 8 '11 at 13:50
Also vacuum and mylar should be written as \mathrm{vacuum} and \mathrm{mylar}. It makes a huge difference. –  Karl Karlsson Jun 8 '11 at 22:01
@Karl: Or \mathit{...}. –  TH. Jun 9 '11 at 12:49

Local modification of the mu-lengths/skips (math-unit skips) could condense the equation enough to avoid the warning yet still produce a consistent enough look to your equation compared to others. Herbert Voß' mathmode document illustrates the different locations where mu-skips are used in an equation:

The default setting for these mu-skips are

\thinmuskip=3mu
\medmuskip=4mu plus 2mu minus 4mu
\thickmuskip=5mu plus 5mu


where 1mu=0.05556em. Perhaps merely adding some shrinkability to \thinmuskip=3mu minus 3mu would help.

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To avoid warning for the case of small overfull (less than 3pt) write the following

\hfuzz = 3pt

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Oh, this is very convenient. I will use this in order to correct the biggest problems first. –  Niriel Mar 22 at 16:44