diff --git a/double_slider.py b/double_slider.py
new file mode 100644
index 0000000..460159c
--- /dev/null
+++ b/double_slider.py
@@ -0,0 +1,33 @@
+from __future__ import division
+from future.builtins import super
+
+from PyQt5.QtWidgets import QSlider
+
+
+class QDoubleSlider(QSlider):
+
+    def __init__(self, parent, min_value, max_value, step, init_value=None):
+        super().__init__(parent)
+        self.min_value = min_value
+        self.max_value = max_value
+        self.step = step
+        self.init_value = init_value
+        self.nvalues = int((max_value - min_value)/step)
+
+        true_max_value = min_value + step*self.nvalues
+        if true_max_value != max_value:
+            self.max_value = true_max_value
+
+        self.setMinimum(self.float_2_int(min_value))
+        self.setMaximum(self.float_2_int(max_value))
+        if init_value is not None:
+            self.setValue(self.float_2_int(init_value))
+
+    def int_2_float(self, value):
+        return (self.max_value - self.min_value)*value/self.nvalues + \
+               self.min_value
+
+    def float_2_int(self, value):
+        return int(
+            self.nvalues*(value - self.min_value) /
+            (self.max_value - self.min_value))
diff --git a/moulder.py b/moulder.py
index 8b24f4e..9fb61e9 100644
--- a/moulder.py
+++ b/moulder.py
@@ -15,6 +15,7 @@ from PyQt5.QtWidgets import QSlider, QHBoxLayout, QLabel, QDialog
 from PyQt5.QtWidgets import QDialogButtonBox, QDoubleSpinBox
 
 from figure_canvas import GravityModelCanvas
+from double_slider import QDoubleSlider
 from interactive import Moulder
 from configure_dialog import ConfigureMeassurementDialog
 
@@ -118,11 +119,9 @@ class MoulderApp(QMainWindow):
         self.density_spinbox.setValue(0)
         self.density_spinbox.setSingleStep(1)
 
-        self.error_slider = QSlider(Qt.Horizontal)
-        self.error_slider.setMinimum(0)
-        self.error_slider.setMaximum(5)
-        self.error_slider.setValue(0)
-        self.error_slider.setTickInterval(0.5)
+        self.error_slider = QDoubleSlider(Qt.Horizontal, 0, 5, 0.5,
+                                          init_value=0)
+        self.error_slider.setTickInterval(self.error_slider.float_2_int(0.5))
         self.error_slider.setTickPosition(QSlider.TicksBelow)
         self.error_spinbox = QDoubleSpinBox()
         self.error_spinbox.setMinimum(0)
@@ -160,10 +159,11 @@ class MoulderApp(QMainWindow):
             self.density_slider.setValue(value)
             self.moulder.set_density(value)
         elif sender == self.error_slider:
+            value = self.error_slider.int_2_float(value)
             self.error_spinbox.setValue(value)
             self.moulder.set_error(value)
         elif sender == self.error_spinbox:
-            self.error_slider.setValue(value)
+            self.error_slider.setValue(self.error_slider.float_2_int(value))
             self.moulder.set_error(value)
 
     def _quit_callback(self):