diff --git a/pyerrors/npr.py b/pyerrors/npr.py
index 16c86442..7ff81cc0 100644
--- a/pyerrors/npr.py
+++ b/pyerrors/npr.py
@@ -91,7 +91,7 @@ def Zq(inv_prop, fermion='Wilson'):
     res = 1 / 12. * np.trace(matmul(inv_prop, np.kron(np.eye(3, dtype=int), p_slash)))
     res.gamma_method()
 
-    if not res.imag.is_zero() and not res.imag.is_zero_within_error(5):
+    if not res.imag.is_zero_within_error(5):
         warnings.warn("Imaginary part of Zq is not zero within 5 sigma")
         return res
     return res.real
diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index 8c03297b..3df41b7a 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -668,12 +668,14 @@ class CObs:
         return self._imag
 
     def gamma_method(self, **kwargs):
+        """Executes the gamma_method for the real and the imaginary part."""
         if isinstance(self.real, Obs):
             self.real.gamma_method(**kwargs)
         if isinstance(self.imag, Obs):
             self.imag.gamma_method(**kwargs)
 
     def is_zero(self):
+        """Checks whether both real and imaginary part are zero within machine precision."""
         return self.real == 0.0 and self.imag == 0.0
 
     def conjugate(self):