diff --git a/docs/dataquality.md b/docs/dataquality.md
index c1ff1fe..054236d 100644
--- a/docs/dataquality.md
+++ b/docs/dataquality.md
@@ -610,10 +610,10 @@ $$
 \begin{flalign}
 \tag{32} \quad
 \frac{\partial \log \mathcal{L}_i}{\partial \sigma_m} = 
-- \frac{\sigma_m ( v_{xx} + v_{yy} + 2 \sigma_m^2)}{D} \times \hspace{8em}\\
-\left( 1 - \frac{v_{xx} ( y - m )^2 - 
+- \frac{\sigma_m ( v_{xx} + v_{yy} + 2 \sigma_m^2)}{D} \times \hspace{16em}\\
+\hspace{8em} \left( 1 - \frac{v_{xx} ( y - m )^2 - 
 2 v_{xy} ( y - m ) ( x - t ) + v_{yy} ( x - t )^2}{D} \right) - \\
-\frac{\sigma_m ( ( x - t )^2 + ( y - m )^2 )}{D} \hspace{10em} &&
+\frac{\sigma_m ( ( x - t )^2 + ( y - m )^2 )}{D} \hspace{16em} &&
 \end{flalign}
 $$