diff --git a/pycast/common/timeseries.py b/pycast/common/timeseries.py
index cbf3be6..4dca477 100644
--- a/pycast/common/timeseries.py
+++ b/pycast/common/timeseries.py
@@ -587,26 +587,30 @@ def apply(self, method):
 
     def sample(self, percentage):
         """Samples with replacement from the TimeSeries. Returns the sample and the remaining timeseries.
-        The original timeseries is not changed
+        The original timeseries is not changed.
 
         :param float percentage: How many percent of the original timeseries should be in the sample
 
-        :return: a tuple containing (sample, rest) as two timeseries objects
+        :return:    A tuple containing (sample, rest) as two TimeSeries.
+        :rtype:     Tuple(TimeSeries,TimeSeries)
 
-        :raise: Raises a ValueError if not 0 < percentage < 1
+        :raise:    Raises a ValueError if percentage is not in (0.0, 1.0).
         """
-        if not (percentage > 0 and percentage < 1):
-            raise ValueError("Parameter percentage has to be in ]0,1[")
+        if not (0.0 < percentage < 1.0):
+            raise ValueError("Parameter percentage has to be in (0.0, 1.0).")
 
-        cls = self.__class__
+        cls         = self.__class__
         value_count = int(len(self) * percentage)
-        values = random.sample(self, value_count)
+        values      = random.sample(self, value_count)
 
-        sample = cls.from_twodim_list(values)
+        sample      = cls.from_twodim_list(values)
         rest_values = self._timeseriesData[:]
+        
         for value in values:
             rest_values.remove(value)
+        
         rest = cls.from_twodim_list(rest_values)
+        
         return sample, rest
 
 class MultiDimensionalTimeSeries(TimeSeries):
diff --git a/pycast/tests/timeseriesmiscellaneoustest.py b/pycast/tests/timeseriesmiscellaneoustest.py
index 7532c8d..77850ad 100644
--- a/pycast/tests/timeseriesmiscellaneoustest.py
+++ b/pycast/tests/timeseriesmiscellaneoustest.py
@@ -391,8 +391,17 @@ def sampling_test(self):
         """Test if the two parts of a sampled timeSeries
         add up to the entire timeSeries"""
         data = [[0.0, 0.0], [1.0, 0.1], [2.0, 0.2], [3.0, 0.3], [4.0, 0.4]]
-        ts = TimeSeries.from_twodim_list(data)
-        sample, rest = ts.sample(.4)
+        ts   = TimeSeries.from_twodim_list(data)
+        
+        for illegalValue in (-3.1, 0.0, 1.0, 1.3, 4.2):
+            try:
+                ts.sample(illegalValue)
+            except ValueError:
+                pass
+            else:
+                assert False, "ValueError not raised. Percentage was %s." % illegalValue    # pragma: no cover
+
+        sample, rest = ts.sample(0.4)
+        
         self.assertEquals(len(sample), 2)
-        self.assertEquals(sample + rest, ts)
-
+        self.assertEquals(sample + rest, ts)
\ No newline at end of file