# [Tex/LaTex] Overfull hbox on a tiny equation

equationswarnings

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 ?

\thinmuskip=3mu

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