diff -r fbf22ccd9d6f -r 0ee888c485d5 Hardware/ISensor.cs
--- a/Hardware/ISensor.cs	Tue Sep 21 10:33:28 2010 +0000
+++ b/Hardware/ISensor.cs	Tue Sep 21 20:32:36 2010 +0000
@@ -52,8 +52,8 @@
   }
 
   public struct SensorValue {
-    private float value;
-    private DateTime time;
+    private readonly float value;
+    private readonly DateTime time;
 
     public SensorValue(float value, DateTime time) {
       this.value = value;