diff --git a/pyerrors/npr.py b/pyerrors/npr.py
index c1641d51..c04813fc 100644
--- a/pyerrors/npr.py
+++ b/pyerrors/npr.py
@@ -95,4 +95,7 @@ def Zq(inv_prop, fermion='Wilson'):
     if not res.imag.is_zero_within_error(5):
         warnings.warn("Imaginary part of Zq is not zero within 5 sigma")
         return res
+    if not np.abs(res.imag.value) <= 1e-6:
+        warnings.warn("Imaginary part of Zq is not smaller than 1e-6")
+        return res
     return res.real
diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index 52192026..7d0b9f24 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -740,6 +740,13 @@ class CObs:
         else:
             return CObs(self.real / other, self.imag / other)
 
+    def __rtruediv__(self, other):
+        r = self.real ** 2 + self.imag ** 2
+        if hasattr(other, 'real') and hasattr(other, 'imag'):
+            return CObs((self.real * other.real + self.imag * other.imag) / r, (self.real * other.imag - self.imag * other.real) / r)
+        else:
+            return CObs(self.real * other / r, -self.imag * other / r)
+
     def __abs__(self):
         return np.sqrt(self.real**2 + self.imag**2)
 
diff --git a/tests/test_pyerrors.py b/tests/test_pyerrors.py
index 39192c6f..9752f093 100644
--- a/tests/test_pyerrors.py
+++ b/tests/test_pyerrors.py
@@ -54,8 +54,12 @@ def test_function_overloading():
         t1 = f([a, b])
         t2 = pe.derived_observable(f, [a, b])
         c = t2 - t1
-        assert c.value == 0.0, str(i)
-        assert np.all(np.abs(c.deltas['e1']) < 1e-14), str(i)
+        assert c.is_zero()
+
+    assert np.log(np.exp(b)) == b
+    assert np.exp(np.log(b)) == b
+    assert np.sqrt(b ** 2) == b
+    assert np.sqrt(b) ** 2 == b
 
 
 def test_overloading_vectorization():
@@ -197,6 +201,7 @@ def test_overloaded_functions():
         assert np.abs((ad_obs.value - item(val)) / ad_obs.value) < 1e-10, item.__name__
         assert np.abs(ad_obs.dvalue - dval * np.abs(deriv[i](val))) < 1e-6, item.__name__
 
+
 def test_utils():
     my_obs = pe.pseudo_Obs(1.0, 0.5, 't')
     my_obs.print(0)
@@ -211,6 +216,7 @@ def test_utils():
     assert my_obs > (my_obs - 1)
     assert my_obs < (my_obs + 1)
 
+
 def test_cobs():
     obs1 = pe.pseudo_Obs(1.0, 0.1, 't')
     obs2 = pe.pseudo_Obs(-0.2, 0.03, 't')
@@ -227,22 +233,22 @@ def test_cobs():
 
     fs = [[lambda x: x[0] + x[1], lambda x: x[1] + x[0]],
           [lambda x: x[0] * x[1], lambda x: x[1] * x[0]]]
-    for other in [1, 1.1, (1.1-0.2j), pe.CObs(obs1), pe.CObs(obs1, obs2)]:
+    for other in [3, 1.1, (1.1 - 0.2j), (2.3 + 0j), (0.0 + 7.7j), pe.CObs(obs1), pe.CObs(obs1, obs2)]:
         for funcs in fs:
             ta = funcs[0]([my_cobs, other])
             tb = funcs[1]([my_cobs, other])
             diff = ta - tb
-            assert np.isclose(0.0, float(diff.real))
-            assert np.isclose(0.0, float(diff.imag))
-            assert np.allclose(0.0, diff.real.deltas['t'])
-            assert np.allclose(0.0, diff.imag.deltas['t'])
+            assert diff.is_zero()
 
         ta = my_cobs - other
         tb = other - my_cobs
         diff = ta + tb
-        assert np.isclose(0.0, float(diff.real))
-        assert np.isclose(0.0, float(diff.imag))
-        assert np.allclose(0.0, diff.real.deltas['t'])
-        assert np.allclose(0.0, diff.imag.deltas['t'])
+        assert diff.is_zero()
+
+        ta = my_cobs / other
+        tb = other / my_cobs
+        diff = ta * tb - 1
+        assert diff.is_zero()
 
         assert (my_cobs / other * other - my_cobs).is_zero()
+        assert (other / my_cobs * my_cobs - other).is_zero()