diff --git a/pyerrors/obs.py b/pyerrors/obs.py
index b83e4f34..c8f4c3e2 100644
--- a/pyerrors/obs.py
+++ b/pyerrors/obs.py
@@ -695,6 +695,15 @@ class Obs:
     def __str__(self):
         return _format_uncertainty(self.value, self._dvalue)
 
+    def __format__(self, format_type):
+        my_str = _format_uncertainty(self.value, self._dvalue,
+                                     significance=int(float(format_type.replace("+", "").replace("-", ""))))
+        for char in ["+", " "]:
+            if format_type.startswith(char):
+                if my_str[0] != "-":
+                    my_str = char + my_str
+        return my_str
+
     def __hash__(self):
         hash_tuple = (np.array([self.value]).astype(np.float32).data.tobytes(),)
         hash_tuple += tuple([o.astype(np.float32).data.tobytes() for o in self.deltas.values()])
@@ -969,17 +978,21 @@ class CObs:
         return 'CObs[' + str(self) + ']'
 
 
-def _format_uncertainty(value, dvalue):
+def _format_uncertainty(value, dvalue, significance=2):
     """Creates a string of a value and its error in paranthesis notation, e.g., 13.02(45)"""
     if dvalue == 0.0:
         return str(value)
+    if not isinstance(significance, int):
+        raise TypeError("significance needs to be an integer.")
+    if significance < 1:
+        raise ValueError("significance needs to be larger than zero.")
     fexp = np.floor(np.log10(dvalue))
     if fexp < 0.0:
-        return '{:{form}}({:2.0f})'.format(value, dvalue * 10 ** (-fexp + 1), form='.' + str(-int(fexp) + 1) + 'f')
+        return '{:{form}}({:1.0f})'.format(value, dvalue * 10 ** (-fexp + significance - 1), form='.' + str(-int(fexp) + significance - 1) + 'f')
     elif fexp == 0.0:
-        return '{:.1f}({:1.1f})'.format(value, dvalue)
+        return f"{value:.{significance - 1}f}({dvalue:1.{significance - 1}f})"
     else:
-        return '{:.0f}({:2.0f})'.format(value, dvalue)
+        return f"{value:.{max(0, int(significance - fexp - 1))}f}({dvalue:2.{max(0, int(significance - fexp - 1))}f})"
 
 
 def _expand_deltas(deltas, idx, shape, gapsize):
diff --git a/tests/obs_test.py b/tests/obs_test.py
index 34c0bb40..02d5b4ac 100644
--- a/tests/obs_test.py
+++ b/tests/obs_test.py
@@ -1213,3 +1213,17 @@ def test_nan_obs():
     o.idl['test'] = [1, 5] + list(range(7, 2002, 2))
     no = np.NaN * o
     no.gamma_method()
+
+
+def test_format_uncertainty():
+    assert pe.obs._format_uncertainty(0.548, 0.248976, 4) == '0.5480(2490)'
+    assert pe.obs._format_uncertainty(0.548, 2.48497, 2) == '0.5(2.5)'
+    assert pe.obs._format_uncertainty(0.548, 2.48497, 4) == '0.548(2.485)'
+    assert pe.obs._format_uncertainty(0.548, 20078.3, 9) == '0.5480(20078.3000)'
+
+
+def test_format():
+    o1 = pe.pseudo_Obs(0.348, 0.0123, "test")
+    assert o1.__format__("+3") == '+0.3480(123)'
+    assert o1.__format__("+2") == '+0.348(12)'
+    assert o1.__format__(" 2") == ' 0.348(12)'