diff --git a/Puffer/module.php b/Puffer/module.php
index eb4aaf1..7cbf4c6 100644
--- a/Puffer/module.php
+++ b/Puffer/module.php
@@ -58,10 +58,10 @@ class Puffer extends IPSModule
 
         $minVT = $this->ReadPropertyInteger("MinVT_Temp");  // z.B. 20
         $maxVT = $this->ReadPropertyInteger("MaxVT_Temp");  // z.B. 80
-        $maxAT = $this->ReadPropertyInteger("MaxAT_Temp");  // z.B. 0
-        $minAT = $this->ReadPropertyInteger("MinAT_Temp");  // z.B. 20
+        $maxAT = $this->ReadPropertyInteger("MaxAT_Temp");  // z.B. 20
+        $minAT = $this->ReadPropertyInteger("MinAT_Temp");  // z.B. 0
 
-        $m = ($minVT - $maxVT) / ($maxAT - $minAT);
+        $m = ($maxVT - $minVT) / ($minAT - $maxAT);
         $this->SetValue("Steigung", $m);