diff --git a/Statistic.h b/Statistic.h
index 55d1365..dddc26f 100644
--- a/Statistic.h
+++ b/Statistic.h
@@ -18,9 +18,9 @@
 class Statistic
 {
 public:
-  Statistic(bool useStdDev = true);                // "switches on/off" stdev run time
-  void     clear(bool useStdDev = true);           // "switches on/off" stdev run time
-  float    add(const float);                       // returns value actually added
+  Statistic(bool useStdDev = true);       // "switches on/off" stdev run time
+  void     clear(bool useStdDev = true) volatile;  // "switches on/off" stdev run time
+  float    add(const float) volatile;              // returns value actually added
 
 
   // returns the number of values added