Overfull hbox on a tiny equation?

Question

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
\begin{equation}
    \theta_2 = \theta_0
\end{equation}
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 ?

Answer 1

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.

Answer 2

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

\hfuzz = 3pt