diff --git a/EMkMachMgr.h b/EMkMachMgr.h
index 923a4d2..d641da6 100644
--- a/EMkMachMgr.h
+++ b/EMkMachMgr.h
@@ -183,10 +183,10 @@ class __declspec( novtable) IMachMgr
       virtual bool SetCurrMachining( int nId) = 0 ;
       virtual bool ResetCurrMachining( void) = 0 ;
       virtual int  GetCurrMachining( void) const = 0 ;
-      virtual bool SetMachiningParam( int nType, bool bVal) = 0 ;
-      virtual bool SetMachiningParam( int nType, int nVal) = 0 ;
-      virtual bool SetMachiningParam( int nType, double dVal) = 0 ;
-      virtual bool SetMachiningParam( int nType, const std::string& sVal) = 0 ;
+      virtual bool SetMachiningParam( int nType, bool bVal, bool* pbChanged = nullptr) = 0 ;
+      virtual bool SetMachiningParam( int nType, int nVal, bool* pbChanged = nullptr) = 0 ;
+      virtual bool SetMachiningParam( int nType, double dVa, bool* pbChanged = nullptr) = 0 ;
+      virtual bool SetMachiningParam( int nType, const std::string& sVal, bool* pbChanged = nullptr) = 0 ;
       virtual bool SetMachiningGeometry( const SELVECTOR& vIds) = 0 ;
       virtual bool MachiningPreview( bool bRecalc) = 0 ;
       virtual bool ExistsMachiningPreview( void) = 0 ;