diff --git a/pyEPR/calcs/back_box_numeric.py b/pyEPR/calcs/back_box_numeric.py
index 8fab76f..b368c00 100644
--- a/pyEPR/calcs/back_box_numeric.py
+++ b/pyEPR/calcs/back_box_numeric.py
@@ -267,7 +267,7 @@ def PT_on_vector(original_vector, original_basis, pertub, energy0, evalue):
 
         def closest_state_to(s):
             def distance(s2):
-                return (s.dag() * s2[1]).norm()
+                return np.abs((s.dag() * s2[1]))
 
             return max(zip(evals, evecs), key=distance)