diff --git a/pyvlx/parameter.py b/pyvlx/parameter.py
index 7df725a6..23454dd9 100644
--- a/pyvlx/parameter.py
+++ b/pyvlx/parameter.py
@@ -193,7 +193,8 @@ def from_percent(position_percent):
     def to_percent(raw):
         """Create percent position value out of raw."""
         # The first byte has the vlue from 0 to 200. Ignoring the second one.
-        return int(raw[0] / 2)
+        # Adding 0.5 allows a slight tolerance for devices (e.g. Velux SML) that do not return exactly 51200 as final position when closed.
+        return int(raw[0] / 2 + 0.5)
 
     def __str__(self):
         """Return string representation of object."""
diff --git a/test/parameter_test.py b/test/parameter_test.py
new file mode 100644
index 00000000..570a55f4
--- /dev/null
+++ b/test/parameter_test.py
@@ -0,0 +1,34 @@
+"""Test for Position class."""
+import unittest
+
+from pyvlx import Parameter, Position
+
+
+class TestParameterPosition(unittest.TestCase):
+    """Test class for Position class."""
+
+    def test_to_percent(self):
+        """Test position percent output from position int input"""
+
+        self.assertEqual(Position.to_percent(Parameter.from_int(0)), 0)
+        self.assertEqual(Position.to_percent(Parameter.from_int(1)), 0)
+        self.assertEqual(Position.to_percent(Parameter.from_int(3)), 0)
+        self.assertEqual(Position.to_percent(Parameter.from_int(256)), 1)
+        self.assertEqual(Position.to_percent(Parameter.from_int(512)), 1)
+        self.assertEqual(Position.to_percent(Parameter.from_int(5120)), 10)
+        self.assertEqual(Position.to_percent(Parameter.from_int(12800)), 25)
+        self.assertEqual(Position.to_percent(Parameter.from_int(25600)), 50)
+        self.assertEqual(Position.to_percent(Parameter.from_int(38400)), 75)
+        self.assertEqual(Position.to_percent(Parameter.from_int(50688)), 99)
+        self.assertEqual(Position.to_percent(Parameter.from_int(51050)), 100)
+        self.assertEqual(Position.to_percent(Parameter.from_int(51200)), 100)
+
+    def test_from_to_percent(self):
+        """Test position percent output from position percent input"""
+        self.assertEqual(Position.to_percent(Position.from_percent(0)), 0)
+        self.assertEqual(Position.to_percent(Position.from_percent(1)), 1)
+        self.assertEqual(Position.to_percent(Position.from_percent(25)), 25)
+        self.assertEqual(Position.to_percent(Position.from_percent(50)), 50)
+        self.assertEqual(Position.to_percent(Position.from_percent(75)), 75)
+        self.assertEqual(Position.to_percent(Position.from_percent(99)), 99)
+        self.assertEqual(Position.to_percent(Position.from_percent(100)), 100)