diff --git a/4 Qualifying Exam/2 Writing/2. QE State of the Art.md b/4 Qualifying Exam/2 Writing/2. QE State of the Art.md
index 89c3f1e0..5109db9e 100644
--- a/4 Qualifying Exam/2 Writing/2. QE State of the Art.md	
+++ b/4 Qualifying Exam/2 Writing/2. QE State of the Art.md	
@@ -27,7 +27,7 @@ $$ \mathcal{P} = \left\{ \frac{1}{(m+e_m)s^2 + (b+e_b)s + (k + e_k)} \right\} \t
 \matrix{m_{min} \leq m+e_m \leq m_{max} \\
 b_{min} \leq b +e_b \leq b_{max} \\
 k_{min} \leq k +e_k \leq k_{max}} $$
-where $e_i$ is the difference between the nominal value of $i$, and the real value on the actual plant. 
+where $e_m$ is the difference between the nominal mass and the actual as-built mass. $e_b$ and $e_k$ follow similar logic.  
 (The disk multiplicative perturbation)
 
 (Explain how actually getting to W_2 isn't really trivial).
\ No newline at end of file