diff --git a/thermopi/screen.py b/thermopi/screen.py
index fdc2f91..80eec5b 100644
--- a/thermopi/screen.py
+++ b/thermopi/screen.py
@@ -15,8 +15,20 @@ class Dial(pygame.sprite.Sprite):
         self.max = (10.0 / 6.0) * PI
         self.min = (8.0 / 6.0) * PI
         self.value = 1
-
+        self.reverse = True
     def update(self):
+        if self.reverse:
+            self.value -= 0.01
+        else:
+            self.value += 0.01
+
+        if self.value < 0:
+            self.value = 0
+            self.reverse = not self.reverse
+        if self.value > 1:
+            self.value = 1
+            self.reverse = not self.reverse
+
         self.image.fill((0, 0, 0))
         pygame.draw.arc(self.image, (255, 255, 255), self.rect, self.min - (self.max * self.value), self.min, 32)