diff --git a/Meade.net.Telescope/ExtensionMethods/DoubelExtensions.cs b/Meade.net.Telescope/ExtensionMethods/DoubelExtensions.cs
new file mode 100644
index 0000000..85567ba
--- /dev/null
+++ b/Meade.net.Telescope/ExtensionMethods/DoubelExtensions.cs
@@ -0,0 +1,10 @@
+namespace System
+{
+    static class DoubelExtensions
+    {
+        public static bool Between(this double value, double lower, double higher)
+        {
+            return value >= lower & value <= higher;
+        }
+    }
+}