Fix typo

docs/src/angle_derivation/refraction_inside_vial_resin.tex

@@ -38,7 +38,7 @@
     \varepsilon = \arccos\left(\frac{x^2 + R_i^2 - R_o^2}{2 R_i x}\right) - \frac{\pi}{2}.
 \end{equation}
 Further, $\beta'=\mathrm{sign}(y) \cdot (\frac{\pi}{2}- \varepsilon)$ and because of refraction $\gamma=\arcsin(\frac{n_\text{vial} \cdot \sin(\beta')}{n_\text{resin}})$. 
-The total ray deflection angles are given by $\delta_1=\alpha - \beta$ and $\delta_2=\beta-\gamma$ resulting in $\delta_\text{ges} = \delta_1 + \delta_2$. 
+The total ray deflection angles are given by $\delta_1=\alpha - \beta$ and $\delta_2=\beta'-\gamma$ resulting in $\delta_\text{ges} = \delta_1 + \delta_2$. 
 
 % $\Delta y$ indicates the height distance the ray propagates because of refraction on the vial interface and is given by $\Delta y = \sin(\delta_1) \cdot x$. 
 % The horizontal distance from beginning of the vial until intersection with the vial is given by $\Delta x = R_o - \sqrt{R_o^2-y^2}$.