endY := FX + startY; 
_x := Parent._prop_LeftMargin + Round(VSpace*((X + (Y - startY)*b) - startX)/FX);
_y := Parent._prop_TopMargin + HSpace;  
MoveTo(_x, _y);
_x := Parent._prop_LeftMargin + Round(VSpace*((X + (Y - endY)*b) - startX)/FX);
_y := Parent._prop_TopMargin;  
LineTo(_x, _y);