diff --git a/EGkSurfTriMesh.h b/EGkSurfTriMesh.h
index 2cd362b..84d3db1 100644
--- a/EGkSurfTriMesh.h
+++ b/EGkSurfTriMesh.h
@@ -70,7 +70,7 @@ class __declspec( novtable) ISurfTriMesh : public ISurf
       virtual double GetSmoothAngle( void) const = 0 ;
       virtual bool GetShowEdges( void) const = 0 ;
       virtual bool GetVertex( int nId, Point3d& ptP) const = 0 ;
-      virtual bool GetVertexParam( int nId, double& dU, double& dV) const = 0 ;
+      virtual bool GetVertexParam( int nId, double& dU, double& dV, bool bDownScaled = true) const = 0 ;
       virtual int  GetFirstVertex( Point3d& ptP) const = 0 ;
       virtual int  GetNextVertex( int nId, Point3d& ptP) const = 0 ;
       virtual bool GetTriangle( int nId, int nIdVert[3]) const = 0 ;