diff --git a/docs/PURE_FORMULAS.md b/docs/PURE_FORMULAS.md
index 99c3194c..0a7176fd 100644
--- a/docs/PURE_FORMULAS.md
+++ b/docs/PURE_FORMULAS.md
@@ -64,6 +64,8 @@ $$\chi > \frac{1}{2} \implies \text{compressive}$$
 
 $$\chi < \frac{1}{2} \implies \text{anti-compressive}$$
 
+$$\chi = \frac{1}{2} \implies \text{critical balance}$$
+
 ---
 
 ## 6. Q16_16