Update algorithm.rst

docs/source/sls/algorithm.rst

@@ -104,9 +104,12 @@ ERR数据单元构造误差数据，该步误差公式：
 
 .. math::
 
-   \sigma = \sqrt{((SCI-bias)+\sigma^2 + readnoise^2)}
-
+\begin{displaymath}
+    v = {\sigma}_1 \cdot {\sigma}_2
+    {\tau}_1 \cdot {\tau}_2
+\end{displaymath}
 
+\sigma = \sqrt{((SCI-bias)+\sigma^2 + readnoise^2)}
 **Dark correction**
 
 class: csst_ms_sls_instrument.steps.DarkCorrStep